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 $72.55   4.173%   $75.5775   $75.58   $75.60   $75.60  
  Purchase #2 $109.33   11.246%   $121.6253   $121.63   $121.65   $121.60  
  Purchase #3 $50.44   10.389%   $55.6802   $55.68   $55.70   $55.70  
  Purchase #4 $223.98   6.233%   $237.9407   $237.94   $237.95   $237.90  
  Purchase #5 $49.53   9.549%   $54.2596   $54.26   $54.25   $54.30  
  Purchase #6 $229.70   3.252%   $237.1698   $237.17   $237.15   $237.20  
  Purchase #7 $160.58   5.652%   $169.656   $169.66   $169.65   $169.70  
  7 purchase totals = $896.11       $951.9091   $951.92   $951.95   $952.00