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 $30.77   8.211%   $33.2965   $33.30   $33.30   $33.30  
  Purchase #2 $216.36   4.872%   $226.9011   $226.90   $226.90   $226.90  
  Purchase #3 $51.51   12.809%   $58.1079   $58.11   $58.10   $58.10  
  Purchase #4 $93.28   3.431%   $96.4804   $96.48   $96.50   $96.50  
  Purchase #5 $207.80   9.736%   $228.0314   $228.03   $228.05   $228.00  
  Purchase #6 $67.47   9.375%   $73.7953   $73.80   $73.80   $73.80  
  Purchase #7 $248.44   7.227%   $266.3948   $266.39   $266.40   $266.40  
  7 purchase totals = $915.63       $983.0074   $983.01   $983.05   $983.00