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 $233.38   13.142%   $264.0508   $264.05   $264.05   $264.10  
  Purchase #2 $200.43   4.569%   $209.5876   $209.59   $209.60   $209.60  
  Purchase #3 $160.98   4.140%   $167.6446   $167.64   $167.65   $167.60  
  Purchase #4 $218.97   10.587%   $242.1524   $242.15   $242.15   $242.20  
  Purchase #5 $59.66   13.547%   $67.7421   $67.74   $67.75   $67.70  
  Purchase #6 $245.82   3.547%   $254.5392   $254.54   $254.55   $254.50  
  Purchase #7 $140.95   5.838%   $149.1787   $149.18   $149.20   $149.20  
  7 purchase totals = $1,260.19       $1,354.8954   $1,354.89   $1,354.95   $1,354.90