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 $188.61   7.258%   $202.2993   $202.30   $202.30   $202.30  
  Purchase #2 $241.53   9.554%   $264.6058   $264.61   $264.60   $264.60  
  Purchase #3 $84.69   9.247%   $92.5213   $92.52   $92.50   $92.50  
  Purchase #4 $139.73   12.795%   $157.6085   $157.61   $157.60   $157.60  
  Purchase #5 $16.43   13.283%   $18.6124   $18.61   $18.60   $18.60  
  Purchase #6 $222.76   11.649%   $248.7093   $248.71   $248.70   $248.70  
  Purchase #7 $47.79   13.241%   $54.1179   $54.12   $54.10   $54.10  
  7 purchase totals = $941.54       $1,038.4745   $1,038.48   $1,038.40   $1,038.40