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 $210.66   10.211%   $232.1705   $232.17   $232.15   $232.20  
  Purchase #2 $94.68   8.484%   $102.7127   $102.71   $102.70   $102.70  
  Purchase #3 $250.88   4.863%   $263.0803   $263.08   $263.10   $263.10  
  Purchase #4 $59.34   10.178%   $65.3796   $65.38   $65.40   $65.40  
  Purchase #5 $77.67   13.362%   $88.0483   $88.05   $88.05   $88.00  
  Purchase #6 $92.50   12.660%   $104.2105   $104.21   $104.20   $104.20  
  Purchase #7 $227.79   6.472%   $242.5326   $242.53   $242.55   $242.50  
  7 purchase totals = $1,013.52       $1,098.1345   $1,098.13   $1,098.15   $1,098.10