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 $64.44   13.292%   $73.0054   $73.01   $73.00   $73.00  
  Purchase #2 $242.83   5.222%   $255.5106   $255.51   $255.50   $255.50  
  Purchase #3 $151.32   11.174%   $168.2285   $168.23   $168.25   $168.20  
  Purchase #4 $46.79   6.213%   $49.6971   $49.70   $49.70   $49.70  
  Purchase #5 $22.60   10.531%   $24.98   $24.98   $25.00   $25.00  
  Purchase #6 $42.41   6.717%   $45.2587   $45.26   $45.25   $45.30  
  Purchase #7 $233.39   10.118%   $257.0044   $257.00   $257.00   $257.00  
  7 purchase totals = $803.78       $873.6847   $873.69   $873.70   $873.70