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 $23.38   5.697%   $24.712   $24.71   $24.70   $24.70  
  Purchase #2 $148.56   11.636%   $165.8464   $165.85   $165.85   $165.80  
  Purchase #3 $136.68   10.549%   $151.0984   $151.10   $151.10   $151.10  
  Purchase #4 $107.56   11.732%   $120.1789   $120.18   $120.20   $120.20  
  Purchase #5 $175.33   9.327%   $191.683   $191.68   $191.70   $191.70  
  Purchase #6 $40.67   13.654%   $46.2231   $46.22   $46.20   $46.20  
  Purchase #7 $118.94   11.588%   $132.7228   $132.72   $132.70   $132.70  
  7 purchase totals = $751.12       $832.4646   $832.46   $832.45   $832.40