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 $238.42   13.202%   $269.8962   $269.90   $269.90   $269.90  
  Purchase #2 $100.69   9.800%   $110.5576   $110.56   $110.55   $110.60  
  Purchase #3 $83.94   5.653%   $88.6851   $88.69   $88.70   $88.70  
  Purchase #4 $214.50   10.303%   $236.5999   $236.60   $236.60   $236.60  
  Purchase #5 $201.50   5.487%   $212.5563   $212.56   $212.55   $212.60  
  Purchase #6 $56.41   12.262%   $63.327   $63.33   $63.35   $63.30  
  Purchase #7 $208.57   3.439%   $215.7427   $215.74   $215.75   $215.70  
  7 purchase totals = $1,104.03       $1,197.3648   $1,197.38   $1,197.40   $1,197.40