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 $139.73   8.776%   $151.9927   $151.99   $152.00   $152.00  
  Purchase #2 $98.62   7.415%   $105.9327   $105.93   $105.95   $105.90  
  Purchase #3 $91.79   7.165%   $98.3668   $98.37   $98.35   $98.40  
  Purchase #4 $64.46   4.661%   $67.4645   $67.46   $67.45   $67.50  
  Purchase #5 $105.67   13.298%   $119.722   $119.72   $119.70   $119.70  
  Purchase #6 $157.98   5.799%   $167.1413   $167.14   $167.15   $167.10  
  Purchase #7 $76.88   9.684%   $84.3251   $84.33   $84.35   $84.30  
  7 purchase totals = $735.13       $794.9451   $794.94   $794.95   $794.90