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 $69.38   4.437%   $72.4584   $72.46   $72.45   $72.50  
  Purchase #2 $241.58   4.659%   $252.8352   $252.84   $252.85   $252.80  
  Purchase #3 $159.29   11.105%   $176.9792   $176.98   $177.00   $177.00  
  Purchase #4 $32.82   4.827%   $34.4042   $34.40   $34.40   $34.40  
  Purchase #5 $91.61   4.174%   $95.4338   $95.43   $95.45   $95.40  
  Purchase #6 $140.29   12.874%   $158.3509   $158.35   $158.35   $158.40  
  Purchase #7 $126.57   4.755%   $132.5884   $132.59   $132.60   $132.60  
  7 purchase totals = $861.54       $923.0501   $923.05   $923.10   $923.10