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 $225.32   7.413%   $242.023   $242.02   $242.00   $242.00  
  Purchase #2 $143.87   9.557%   $157.6197   $157.62   $157.60   $157.60  
  Purchase #3 $225.54   9.350%   $246.628   $246.63   $246.65   $246.60  
  Purchase #4 $120.34   10.716%   $133.2356   $133.24   $133.25   $133.20  
  Purchase #5 $53.61   10.762%   $59.3795   $59.38   $59.40   $59.40  
  Purchase #6 $234.93   4.131%   $244.635   $244.64   $244.65   $244.60  
  Purchase #7 $43.78   13.732%   $49.7919   $49.79   $49.80   $49.80  
  7 purchase totals = $1,047.39       $1,133.3127   $1,133.32   $1,133.35   $1,133.20