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 $22.26   11.303%   $24.776   $24.78   $24.80   $24.80  
  Purchase #2 $80.67   11.168%   $89.6792   $89.68   $89.70   $89.70  
  Purchase #3 $145.98   4.238%   $152.1666   $152.17   $152.15   $152.20  
  Purchase #4 $54.97   5.768%   $58.1407   $58.14   $58.15   $58.10  
  Purchase #5 $85.72   8.785%   $93.2505   $93.25   $93.25   $93.30  
  Purchase #6 $217.78   8.728%   $236.7878   $236.79   $236.80   $236.80  
  Purchase #7 $242.63   6.784%   $259.09   $259.09   $259.10   $259.10  
  7 purchase totals = $850.01       $913.8908   $913.90   $913.95   $914.00