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 $236.57   10.754%   $262.0107   $262.01   $262.00   $262.00  
  Purchase #2 $25.72   6.413%   $27.3694   $27.37   $27.35   $27.40  
  Purchase #3 $178.99   6.865%   $191.2777   $191.28   $191.30   $191.30  
  Purchase #4 $11.65   10.223%   $12.841   $12.84   $12.85   $12.80  
  Purchase #5 $50.94   10.730%   $56.4059   $56.41   $56.40   $56.40  
  Purchase #6 $141.76   11.222%   $157.6683   $157.67   $157.65   $157.70  
  Purchase #7 $117.42   5.712%   $124.127   $124.13   $124.15   $124.10  
  7 purchase totals = $763.05       $831.7000   $831.71   $831.70   $831.70