Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $175.41   9.308%   $191.7372   $191.74   $191.75   $191.70  
  Purchase #2 $218.67   11.543%   $243.9111   $243.91   $243.90   $243.90  
  Purchase #3 $211.71   11.177%   $235.3728   $235.37   $235.35   $235.40  
  Purchase #4 $154.71   12.137%   $173.4872   $173.49   $173.50   $173.50  
  Purchase #5 $185.41   8.535%   $201.2347   $201.23   $201.25   $201.20  
  Purchase #6 $158.67   13.595%   $180.2412   $180.24   $180.25   $180.20  
  Purchase #7 $133.36   12.729%   $150.3354   $150.34   $150.35   $150.30  
  7 purchase totals = $1,237.94       $1,376.3196   $1,376.32   $1,376.35   $1,376.20