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 $90.85   4.685%   $95.1063   $95.11   $95.10   $95.10  
  Purchase #2 $123.88   6.514%   $131.9495   $131.95   $131.95   $131.90  
  Purchase #3 $162.45   9.467%   $177.8291   $177.83   $177.85   $177.80  
  Purchase #4 $237.66   9.690%   $260.6893   $260.69   $260.70   $260.70  
  Purchase #5 $54.98   5.386%   $57.9412   $57.94   $57.95   $57.90  
  Purchase #6 $148.84   11.537%   $166.0117   $166.01   $166.00   $166.00  
  Purchase #7 $83.66   12.579%   $94.1836   $94.18   $94.20   $94.20  
  7 purchase totals = $902.32       $983.7107   $983.71   $983.75   $983.60