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 $68.79   9.319%   $75.2005   $75.20   $75.20   $75.20  
  Purchase #2 $211.73   11.823%   $236.7628   $236.76   $236.75   $236.80  
  Purchase #3 $89.78   7.687%   $96.6814   $96.68   $96.70   $96.70  
  Purchase #4 $232.57   11.198%   $258.6132   $258.61   $258.60   $258.60  
  Purchase #5 $44.51   5.814%   $47.0978   $47.10   $47.10   $47.10  
  Purchase #6 $95.54   3.139%   $98.539   $98.54   $98.55   $98.50  
  Purchase #7 $130.67   10.573%   $144.4857   $144.49   $144.50   $144.50  
  7 purchase totals = $873.59       $957.3804   $957.38   $957.40   $957.40