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 $227.98   3.652%   $236.3058   $236.31   $236.30   $236.30  
  Purchase #2 $24.42   12.216%   $27.4031   $27.40   $27.40   $27.40  
  Purchase #3 $179.88   7.211%   $192.8511   $192.85   $192.85   $192.90  
  Purchase #4 $126.72   8.661%   $137.6952   $137.70   $137.70   $137.70  
  Purchase #5 $233.42   11.544%   $260.366   $260.37   $260.35   $260.40  
  Purchase #6 $115.49   5.128%   $121.4123   $121.41   $121.40   $121.40  
  Purchase #7 $85.53   7.314%   $91.7857   $91.79   $91.80   $91.80  
  7 purchase totals = $993.44       $1,067.8192   $1,067.83   $1,067.80   $1,067.90