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 $154.73   4.651%   $161.9265   $161.93   $161.95   $161.90  
  Purchase #2 $180.51   8.569%   $195.9779   $195.98   $196.00   $196.00  
  Purchase #3 $61.26   8.299%   $66.344   $66.34   $66.35   $66.30  
  Purchase #4 $107.63   7.302%   $115.4891   $115.49   $115.50   $115.50  
  Purchase #5 $156.57   12.402%   $175.9878   $175.99   $176.00   $176.00  
  Purchase #6 $64.63   6.207%   $68.6416   $68.64   $68.65   $68.60  
  Purchase #7 $250.74   8.447%   $271.92   $271.92   $271.90   $271.90  
  7 purchase totals = $976.07       $1,056.2869   $1,056.29   $1,056.35   $1,056.20