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 $66.76   13.227%   $75.5903   $75.59   $75.60   $75.60  
  Purchase #2 $111.79   6.216%   $118.7389   $118.74   $118.75   $118.70  
  Purchase #3 $60.68   10.369%   $66.9719   $66.97   $66.95   $67.00  
  Purchase #4 $244.63   3.221%   $252.5095   $252.51   $252.50   $252.50  
  Purchase #5 $19.71   8.186%   $21.3235   $21.32   $21.30   $21.30  
  Purchase #6 $114.92   4.465%   $120.0512   $120.05   $120.05   $120.10  
  Purchase #7 $77.82   6.613%   $82.9662   $82.97   $82.95   $83.00  
  7 purchase totals = $696.31       $738.1515   $738.15   $738.10   $738.20