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 $244.39   5.179%   $257.047   $257.05   $257.05   $257.00  
  Purchase #2 $211.50   8.716%   $229.9343   $229.93   $229.95   $229.90  
  Purchase #3 $37.96   9.773%   $41.6698   $41.67   $41.65   $41.70  
  Purchase #4 $162.66   12.807%   $183.4919   $183.49   $183.50   $183.50  
  Purchase #5 $71.38   5.684%   $75.4372   $75.44   $75.45   $75.40  
  Purchase #6 $233.37   12.465%   $262.4596   $262.46   $262.45   $262.50  
  Purchase #7 $95.42   8.220%   $103.2635   $103.26   $103.25   $103.30  
  7 purchase totals = $1,056.68       $1,153.3033   $1,153.30   $1,153.30   $1,153.30