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 $88.65   13.629%   $100.7321   $100.73   $100.75   $100.70  
  Purchase #2 $86.38   6.793%   $92.2478   $92.25   $92.25   $92.20  
  Purchase #3 $141.65   5.814%   $149.8855   $149.89   $149.90   $149.90  
  Purchase #4 $218.77   6.448%   $232.8763   $232.88   $232.90   $232.90  
  Purchase #5 $155.46   3.741%   $161.2758   $161.28   $161.30   $161.30  
  Purchase #6 $243.31   7.441%   $261.4147   $261.41   $261.40   $261.40  
  Purchase #7 $143.40   11.653%   $160.1104   $160.11   $160.10   $160.10  
  7 purchase totals = $1,077.62       $1,158.5426   $1,158.55   $1,158.60   $1,158.50