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 $65.51   6.332%   $69.6581   $69.66   $69.65   $69.70  
  Purchase #2 $126.73   4.475%   $132.4012   $132.40   $132.40   $132.40  
  Purchase #3 $119.67   5.161%   $125.8462   $125.85   $125.85   $125.80  
  Purchase #4 $206.94   3.194%   $213.5497   $213.55   $213.55   $213.50  
  Purchase #5 $64.44   6.321%   $68.5133   $68.51   $68.50   $68.50  
  Purchase #6 $163.62   6.228%   $173.8103   $173.81   $173.80   $173.80  
  Purchase #7 $90.34   7.764%   $97.354   $97.35   $97.35   $97.40  
  7 purchase totals = $837.25       $881.1328   $881.13   $881.10   $881.10