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 $41.59   11.870%   $46.5267   $46.53   $46.55   $46.50  
  Purchase #2 $195.52   9.159%   $213.4277   $213.43   $213.45   $213.40  
  Purchase #3 $93.97   8.326%   $101.7939   $101.79   $101.80   $101.80  
  Purchase #4 $239.63   11.209%   $266.4901   $266.49   $266.50   $266.50  
  Purchase #5 $189.62   12.470%   $213.2656   $213.27   $213.25   $213.30  
  Purchase #6 $67.44   12.494%   $75.866   $75.87   $75.85   $75.90  
  Purchase #7 $49.64   13.140%   $56.1627   $56.16   $56.15   $56.20  
  7 purchase totals = $877.41       $973.5327   $973.54   $973.55   $973.60