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 $211.62   10.475%   $233.7872   $233.79   $233.80   $233.80  
  Purchase #2 $234.98   13.203%   $266.0044   $266.00   $266.00   $266.00  
  Purchase #3 $20.88   7.422%   $22.4297   $22.43   $22.45   $22.40  
  Purchase #4 $102.92   5.318%   $108.3933   $108.39   $108.40   $108.40  
  Purchase #5 $187.93   10.716%   $208.0686   $208.07   $208.05   $208.10  
  Purchase #6 $228.94   8.110%   $247.507   $247.51   $247.50   $247.50  
  Purchase #7 $69.77   3.504%   $72.2147   $72.21   $72.20   $72.20  
  7 purchase totals = $1,057.04       $1,158.4049   $1,158.40   $1,158.40   $1,158.40