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 $216.90   3.494%   $224.4785   $224.48   $224.50   $224.50  
  Purchase #2 $136.48   3.271%   $140.9443   $140.94   $140.95   $140.90  
  Purchase #3 $232.74   11.843%   $260.3034   $260.30   $260.30   $260.30  
  Purchase #4 $191.63   5.397%   $201.9723   $201.97   $201.95   $202.00  
  Purchase #5 $118.36   12.287%   $132.9029   $132.90   $132.90   $132.90  
  Purchase #6 $161.35   3.220%   $166.5455   $166.55   $166.55   $166.50  
  Purchase #7 $186.28   3.467%   $192.7383   $192.74   $192.75   $192.70  
  7 purchase totals = $1,243.74       $1,319.8852   $1,319.88   $1,319.90   $1,319.80