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 $218.52   11.181%   $242.9527   $242.95   $242.95   $243.00  
  Purchase #2 $197.39   11.216%   $219.5293   $219.53   $219.55   $219.50  
  Purchase #3 $177.56   11.364%   $197.7379   $197.74   $197.75   $197.70  
  Purchase #4 $81.61   13.646%   $92.7465   $92.75   $92.75   $92.70  
  Purchase #5 $152.33   3.394%   $157.5001   $157.50   $157.50   $157.50  
  Purchase #6 $242.69   5.199%   $255.3075   $255.31   $255.30   $255.30  
  Purchase #7 $114.40   4.145%   $119.1419   $119.14   $119.15   $119.10  
  7 purchase totals = $1,184.50       $1,284.9159   $1,284.92   $1,284.95   $1,284.80