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 $84.86   3.293%   $87.6544   $87.65   $87.65   $87.70  
  Purchase #2 $241.78   8.740%   $262.9116   $262.91   $262.90   $262.90  
  Purchase #3 $106.64   13.786%   $121.3414   $121.34   $121.35   $121.30  
  Purchase #4 $87.98   11.576%   $98.1646   $98.16   $98.15   $98.20  
  Purchase #5 $56.62   13.339%   $64.1725   $64.17   $64.15   $64.20  
  Purchase #6 $139.73   6.673%   $149.0542   $149.05   $149.05   $149.10  
  Purchase #7 $158.64   5.434%   $167.2605   $167.26   $167.25   $167.30  
  7 purchase totals = $876.25       $950.5592   $950.54   $950.50   $950.70