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 $44.76   13.760%   $50.919   $50.92   $50.90   $50.90  
  Purchase #2 $85.43   3.298%   $88.2475   $88.25   $88.25   $88.20  
  Purchase #3 $52.44   6.824%   $56.0185   $56.02   $56.00   $56.00  
  Purchase #4 $241.55   9.812%   $265.2509   $265.25   $265.25   $265.30  
  Purchase #5 $239.72   13.669%   $272.4873   $272.49   $272.50   $272.50  
  Purchase #6 $192.96   11.816%   $215.7602   $215.76   $215.75   $215.80  
  Purchase #7 $30.92   9.159%   $33.752   $33.75   $33.75   $33.80  
  7 purchase totals = $887.78       $982.4354   $982.44   $982.40   $982.50