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 $195.67   4.315%   $204.1132   $204.11   $204.10   $204.10  
  Purchase #2 $134.53   13.830%   $153.1355   $153.14   $153.15   $153.10  
  Purchase #3 $137.70   8.602%   $149.545   $149.55   $149.55   $149.50  
  Purchase #4 $33.40   7.581%   $35.9321   $35.93   $35.95   $35.90  
  Purchase #5 $100.62   10.167%   $110.85   $110.85   $110.85   $110.90  
  Purchase #6 $58.78   9.572%   $64.4064   $64.41   $64.40   $64.40  
  Purchase #7 $235.88   13.456%   $267.62   $267.62   $267.60   $267.60  
  7 purchase totals = $896.58       $985.6022   $985.61   $985.60   $985.50