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 $208.31   4.533%   $217.7527   $217.75   $217.75   $217.80  
  Purchase #2 $161.35   3.266%   $166.6197   $166.62   $166.60   $166.60  
  Purchase #3 $126.47   8.380%   $137.0682   $137.07   $137.05   $137.10  
  Purchase #4 $47.95   11.715%   $53.5673   $53.57   $53.55   $53.60  
  Purchase #5 $86.62   5.784%   $91.6301   $91.63   $91.65   $91.60  
  Purchase #6 $82.95   3.796%   $86.0988   $86.10   $86.10   $86.10  
  Purchase #7 $245.30   10.390%   $270.7867   $270.79   $270.80   $270.80  
  7 purchase totals = $958.95       $1,023.5235   $1,023.53   $1,023.50   $1,023.60