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 $77.51   12.453%   $87.1623   $87.16   $87.15   $87.20  
  Purchase #2 $100.75   3.574%   $104.3508   $104.35   $104.35   $104.40  
  Purchase #3 $84.47   13.814%   $96.1387   $96.14   $96.15   $96.10  
  Purchase #4 $176.78   13.733%   $201.0572   $201.06   $201.05   $201.10  
  Purchase #5 $59.58   8.583%   $64.6938   $64.69   $64.70   $64.70  
  Purchase #6 $9.73   10.484%   $10.7501   $10.75   $10.75   $10.80  
  Purchase #7 $171.37   5.398%   $180.6206   $180.62   $180.60   $180.60  
  7 purchase totals = $680.19       $744.7735   $744.77   $744.75   $744.90