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 $217.28   11.656%   $242.6062   $242.61   $242.60   $242.60  
  Purchase #2 $32.44   9.209%   $35.4274   $35.43   $35.45   $35.40  
  Purchase #3 $15.58   3.581%   $16.1379   $16.14   $16.15   $16.10  
  Purchase #4 $191.79   5.208%   $201.7784   $201.78   $201.80   $201.80  
  Purchase #5 $104.49   11.508%   $116.5147   $116.51   $116.50   $116.50  
  Purchase #6 $152.37   6.150%   $161.7408   $161.74   $161.75   $161.70  
  Purchase #7 $241.47   7.867%   $260.4664   $260.47   $260.45   $260.50  
  7 purchase totals = $955.42       $1,034.6718   $1,034.68   $1,034.70   $1,034.60