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 $14.36   4.677%   $15.0316   $15.03   $15.05   $15.00  
  Purchase #2 $29.71   8.399%   $32.2053   $32.21   $32.20   $32.20  
  Purchase #3 $118.36   8.471%   $128.3863   $128.39   $128.40   $128.40  
  Purchase #4 $206.31   5.134%   $216.902   $216.90   $216.90   $216.90  
  Purchase #5 $225.47   9.787%   $247.5367   $247.54   $247.55   $247.50  
  Purchase #6 $121.90   5.313%   $128.3765   $128.38   $128.40   $128.40  
  Purchase #7 $241.80   5.532%   $255.1764   $255.18   $255.20   $255.20  
  7 purchase totals = $957.91       $1,023.6148   $1,023.63   $1,023.70   $1,023.60