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 $246.65   7.205%   $264.4211   $264.42   $264.40   $264.40  
  Purchase #2 $118.99   13.673%   $135.2595   $135.26   $135.25   $135.30  
  Purchase #3 $229.98   5.257%   $242.07   $242.07   $242.05   $242.10  
  Purchase #4 $26.60   10.831%   $29.481   $29.48   $29.50   $29.50  
  Purchase #5 $195.72   8.625%   $212.6009   $212.60   $212.60   $212.60  
  Purchase #6 $158.89   8.491%   $172.3813   $172.38   $172.40   $172.40  
  Purchase #7 $235.63   3.437%   $243.7286   $243.73   $243.75   $243.70  
  7 purchase totals = $1,212.46       $1,299.9424   $1,299.94   $1,299.95   $1,300.00