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 $56.86   4.690%   $59.5267   $59.53   $59.55   $59.50  
  Purchase #2 $213.90   3.452%   $221.2838   $221.28   $221.30   $221.30  
  Purchase #3 $218.63   12.821%   $246.6606   $246.66   $246.65   $246.70  
  Purchase #4 $74.94   12.180%   $84.0677   $84.07   $84.05   $84.10  
  Purchase #5 $222.40   7.845%   $239.8473   $239.85   $239.85   $239.80  
  Purchase #6 $82.30   4.821%   $86.2677   $86.27   $86.25   $86.30  
  Purchase #7 $5.75   6.694%   $6.1349   $6.13   $6.15   $6.10  
  7 purchase totals = $874.78       $943.7887   $943.79   $943.80   $943.80