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 $64.63   13.819%   $73.5612   $73.56   $73.55   $73.60  
  Purchase #2 $86.86   6.477%   $92.4859   $92.49   $92.50   $92.50  
  Purchase #3 $10.58   6.595%   $11.2778   $11.28   $11.30   $11.30  
  Purchase #4 $105.39   6.492%   $112.2319   $112.23   $112.25   $112.20  
  Purchase #5 $124.43   7.214%   $133.4064   $133.41   $133.40   $133.40  
  Purchase #6 $225.53   11.443%   $251.3374   $251.34   $251.35   $251.30  
  Purchase #7 $95.69   6.868%   $102.262   $102.26   $102.25   $102.30  
  7 purchase totals = $713.11       $776.5626   $776.57   $776.60   $776.60