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 $40.93   6.473%   $43.5794   $43.58   $43.60   $43.60  
  Purchase #2 $85.60   12.162%   $96.0107   $96.01   $96.00   $96.00  
  Purchase #3 $42.71   6.509%   $45.49   $45.49   $45.50   $45.50  
  Purchase #4 $175.29   4.428%   $183.0518   $183.05   $183.05   $183.10  
  Purchase #5 $222.39   11.330%   $247.5868   $247.59   $247.60   $247.60  
  Purchase #6 $166.87   9.549%   $182.8044   $182.80   $182.80   $182.80  
  Purchase #7 $27.32   9.639%   $29.9534   $29.95   $29.95   $30.00  
  7 purchase totals = $761.11       $828.4765   $828.47   $828.50   $828.60