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 $165.26   12.372%   $185.706   $185.71   $185.70   $185.70  
  Purchase #2 $68.97   10.441%   $76.1712   $76.17   $76.15   $76.20  
  Purchase #3 $183.94   3.559%   $190.4864   $190.49   $190.50   $190.50  
  Purchase #4 $48.84   8.410%   $52.9474   $52.95   $52.95   $52.90  
  Purchase #5 $97.97   13.220%   $110.9216   $110.92   $110.90   $110.90  
  Purchase #6 $120.70   4.382%   $125.9891   $125.99   $126.00   $126.00  
  Purchase #7 $128.48   3.695%   $133.2273   $133.23   $133.25   $133.20  
  7 purchase totals = $814.16       $875.4490   $875.46   $875.45   $875.40