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 $163.75   6.281%   $174.0351   $174.04   $174.05   $174.00  
  Purchase #2 $202.78   7.696%   $218.3859   $218.39   $218.40   $218.40  
  Purchase #3 $98.33   4.459%   $102.7145   $102.71   $102.70   $102.70  
  Purchase #4 $239.97   12.354%   $269.6159   $269.62   $269.60   $269.60  
  Purchase #5 $202.97   4.353%   $211.8053   $211.81   $211.80   $211.80  
  Purchase #6 $123.77   12.733%   $139.5296   $139.53   $139.55   $139.50  
  Purchase #7 $127.36   13.400%   $144.4262   $144.43   $144.45   $144.40  
  7 purchase totals = $1,158.93       $1,260.5125   $1,260.53   $1,260.55   $1,260.40