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 $208.65   11.340%   $232.3109   $232.31   $232.30   $232.30  
  Purchase #2 $82.65   7.228%   $88.6239   $88.62   $88.60   $88.60  
  Purchase #3 $179.32   13.851%   $204.1576   $204.16   $204.15   $204.20  
  Purchase #4 $54.56   6.210%   $57.9482   $57.95   $57.95   $57.90  
  Purchase #5 $138.94   12.481%   $156.2811   $156.28   $156.30   $156.30  
  Purchase #6 $13.95   3.546%   $14.4447   $14.44   $14.45   $14.40  
  Purchase #7 $182.75   8.411%   $198.1211   $198.12   $198.10   $198.10  
  7 purchase totals = $860.82       $951.8875   $951.88   $951.85   $951.80