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 $11.53   8.275%   $12.4841   $12.48   $12.50   $12.50  
  Purchase #2 $228.94   3.316%   $236.5317   $236.53   $236.55   $236.50  
  Purchase #3 $60.89   10.350%   $67.1921   $67.19   $67.20   $67.20  
  Purchase #4 $244.50   4.505%   $255.5147   $255.51   $255.50   $255.50  
  Purchase #5 $191.45   13.734%   $217.7437   $217.74   $217.75   $217.70  
  Purchase #6 $226.58   9.691%   $248.5379   $248.54   $248.55   $248.50  
  Purchase #7 $155.46   3.315%   $160.6135   $160.61   $160.60   $160.60  
  7 purchase totals = $1,119.35       $1,198.6177   $1,198.60   $1,198.65   $1,198.50