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 $73.25   3.718%   $75.9734   $75.97   $75.95   $76.00  
  Purchase #2 $14.53   7.727%   $15.6527   $15.65   $15.65   $15.70  
  Purchase #3 $124.89   6.295%   $132.7518   $132.75   $132.75   $132.80  
  Purchase #4 $89.28   11.589%   $99.6267   $99.63   $99.65   $99.60  
  Purchase #5 $127.73   9.167%   $139.439   $139.44   $139.45   $139.40  
  Purchase #6 $104.80   9.654%   $114.9174   $114.92   $114.90   $114.90  
  Purchase #7 $169.28   8.662%   $183.943   $183.94   $183.95   $183.90  
  7 purchase totals = $703.76       $762.3040   $762.30   $762.30   $762.30