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 $38.95   9.532%   $42.6627   $42.66   $42.65   $42.70  
  Purchase #2 $205.49   10.130%   $226.3061   $226.31   $226.30   $226.30  
  Purchase #3 $234.70   13.136%   $265.5302   $265.53   $265.55   $265.50  
  Purchase #4 $125.89   8.382%   $136.4421   $136.44   $136.45   $136.40  
  Purchase #5 $111.80   3.369%   $115.5665   $115.57   $115.55   $115.60  
  Purchase #6 $209.29   4.825%   $219.3882   $219.39   $219.40   $219.40  
  Purchase #7 $210.73   4.720%   $220.6765   $220.68   $220.70   $220.70  
  7 purchase totals = $1,136.85       $1,226.5723   $1,226.58   $1,226.60   $1,226.60