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 $115.57   3.402%   $119.5017   $119.50   $119.50   $119.50  
  Purchase #2 $222.45   8.666%   $241.7275   $241.73   $241.75   $241.70  
  Purchase #3 $205.27   13.515%   $233.0122   $233.01   $233.00   $233.00  
  Purchase #4 $194.46   3.676%   $201.6083   $201.61   $201.60   $201.60  
  Purchase #5 $93.32   12.479%   $104.9654   $104.97   $104.95   $105.00  
  Purchase #6 $110.63   9.837%   $121.5127   $121.51   $121.50   $121.50  
  Purchase #7 $120.71   12.659%   $135.9907   $135.99   $136.00   $136.00  
  7 purchase totals = $1,062.41       $1,158.3185   $1,158.32   $1,158.30   $1,158.30