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 $107.43   10.799%   $119.0314   $119.03   $119.05   $119.00  
  Purchase #2 $220.53   11.779%   $246.5062   $246.51   $246.50   $246.50  
  Purchase #3 $235.57   7.146%   $252.4038   $252.40   $252.40   $252.40  
  Purchase #4 $39.61   3.779%   $41.1069   $41.11   $41.10   $41.10  
  Purchase #5 $12.47   11.712%   $13.9305   $13.93   $13.95   $13.90  
  Purchase #6 $62.77   11.566%   $70.03   $70.03   $70.05   $70.00  
  Purchase #7 $188.71   9.812%   $207.2262   $207.23   $207.25   $207.20  
  7 purchase totals = $867.09       $950.2350   $950.24   $950.30   $950.10