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 $68.97   12.185%   $77.374   $77.37   $77.35   $77.40  
  Purchase #2 $191.34   9.140%   $208.8285   $208.83   $208.85   $208.80  
  Purchase #3 $48.41   12.579%   $54.4995   $54.50   $54.50   $54.50  
  Purchase #4 $223.29   12.728%   $251.7104   $251.71   $251.70   $251.70  
  Purchase #5 $24.79   9.396%   $27.1193   $27.12   $27.10   $27.10  
  Purchase #6 $110.34   4.749%   $115.58   $115.58   $115.60   $115.60  
  Purchase #7 $92.65   5.110%   $97.3844   $97.38   $97.40   $97.40  
  7 purchase totals = $759.79       $832.4961   $832.49   $832.50   $832.50