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 $219.26   13.523%   $248.9105   $248.91   $248.90   $248.90  
  Purchase #2 $24.42   3.175%   $25.1953   $25.20   $25.20   $25.20  
  Purchase #3 $236.48   5.705%   $249.9712   $249.97   $249.95   $250.00  
  Purchase #4 $147.76   4.479%   $154.3782   $154.38   $154.40   $154.40  
  Purchase #5 $108.59   11.439%   $121.0116   $121.01   $121.00   $121.00  
  Purchase #6 $123.58   10.193%   $136.1765   $136.18   $136.20   $136.20  
  Purchase #7 $71.74   6.604%   $76.4777   $76.48   $76.50   $76.50  
  7 purchase totals = $931.83       $1,012.1210   $1,012.13   $1,012.15   $1,012.20