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 $62.41   5.761%   $66.0054   $66.01   $66.00   $66.00  
  Purchase #2 $67.87   11.425%   $75.6241   $75.62   $75.60   $75.60  
  Purchase #3 $32.32   10.276%   $35.6412   $35.64   $35.65   $35.60  
  Purchase #4 $218.55   13.621%   $248.3187   $248.32   $248.30   $248.30  
  Purchase #5 $73.70   11.844%   $82.429   $82.43   $82.45   $82.40  
  Purchase #6 $71.83   6.842%   $76.7446   $76.74   $76.75   $76.70  
  Purchase #7 $153.51   7.590%   $165.1614   $165.16   $165.15   $165.20  
  7 purchase totals = $680.19       $749.9244   $749.92   $749.90   $749.80