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 $236.93   3.109%   $244.2962   $244.30   $244.30   $244.30  
  Purchase #2 $213.41   4.290%   $222.5653   $222.57   $222.55   $222.60  
  Purchase #3 $119.64   12.436%   $134.5184   $134.52   $134.50   $134.50  
  Purchase #4 $230.60   5.179%   $242.5428   $242.54   $242.55   $242.50  
  Purchase #5 $98.97   13.119%   $111.9539   $111.95   $111.95   $112.00  
  Purchase #6 $144.50   11.401%   $160.9744   $160.97   $160.95   $161.00  
  Purchase #7 $132.31   8.280%   $143.2653   $143.27   $143.25   $143.30  
  7 purchase totals = $1,176.36       $1,260.1163   $1,260.12   $1,260.05   $1,260.20