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 $224.42   3.528%   $232.3375   $232.34   $232.35   $232.30  
  Purchase #2 $124.89   6.364%   $132.838   $132.84   $132.85   $132.80  
  Purchase #3 $31.65   10.646%   $35.0195   $35.02   $35.00   $35.00  
  Purchase #4 $178.81   3.859%   $185.7103   $185.71   $185.70   $185.70  
  Purchase #5 $96.53   3.346%   $99.7599   $99.76   $99.75   $99.80  
  Purchase #6 $5.87   7.287%   $6.2977   $6.30   $6.30   $6.30  
  Purchase #7 $119.67   11.809%   $133.8018   $133.80   $133.80   $133.80  
  7 purchase totals = $781.84       $825.7647   $825.77   $825.75   $825.70