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 $141.73   9.541%   $155.2525   $155.25   $155.25   $155.30  
  Purchase #2 $121.99   8.644%   $132.5348   $132.53   $132.55   $132.50  
  Purchase #3 $87.76   12.571%   $98.7923   $98.79   $98.80   $98.80  
  Purchase #4 $169.32   5.505%   $178.6411   $178.64   $178.65   $178.60  
  Purchase #5 $208.44   3.139%   $214.9829   $214.98   $215.00   $215.00  
  Purchase #6 $178.41   11.268%   $198.5132   $198.51   $198.50   $198.50  
  Purchase #7 $47.45   12.872%   $53.5578   $53.56   $53.55   $53.60  
  7 purchase totals = $955.10       $1,032.2746   $1,032.26   $1,032.30   $1,032.30