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 $181.85   13.548%   $206.487   $206.49   $206.50   $206.50  
  Purchase #2 $18.28   11.354%   $20.3555   $20.36   $20.35   $20.40  
  Purchase #3 $152.81   13.358%   $173.2224   $173.22   $173.20   $173.20  
  Purchase #4 $202.73   3.517%   $209.86   $209.86   $209.85   $209.90  
  Purchase #5 $193.81   7.814%   $208.9543   $208.95   $208.95   $209.00  
  Purchase #6 $41.75   9.749%   $45.8202   $45.82   $45.80   $45.80  
  Purchase #7 $79.57   10.833%   $88.1898   $88.19   $88.20   $88.20  
  7 purchase totals = $870.80       $952.8892   $952.89   $952.85   $953.00