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 $67.85   13.507%   $77.0145   $77.01   $77.00   $77.00  
  Purchase #2 $82.77   11.529%   $92.3126   $92.31   $92.30   $92.30  
  Purchase #3 $26.93   10.223%   $29.6831   $29.68   $29.70   $29.70  
  Purchase #4 $118.56   5.733%   $125.357   $125.36   $125.35   $125.40  
  Purchase #5 $126.75   6.414%   $134.8797   $134.88   $134.90   $134.90  
  Purchase #6 $148.42   10.824%   $164.485   $164.49   $164.50   $164.50  
  Purchase #7 $70.41   7.191%   $75.4732   $75.47   $75.45   $75.50  
  7 purchase totals = $641.69       $699.2051   $699.20   $699.20   $699.30