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 $34.94   3.442%   $36.1426   $36.14   $36.15   $36.10  
  Purchase #2 $121.55   3.210%   $125.4518   $125.45   $125.45   $125.50  
  Purchase #3 $224.65   9.551%   $246.1063   $246.11   $246.10   $246.10  
  Purchase #4 $245.56   12.296%   $275.7541   $275.75   $275.75   $275.80  
  Purchase #5 $85.87   11.335%   $95.6034   $95.60   $95.60   $95.60  
  Purchase #6 $134.72   13.278%   $152.6081   $152.61   $152.60   $152.60  
  Purchase #7 $58.29   12.131%   $65.3612   $65.36   $65.35   $65.40  
  7 purchase totals = $905.58       $997.0275   $997.02   $997.00   $997.10