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 $36.77   12.333%   $41.3048   $41.30   $41.30   $41.30  
  Purchase #2 $195.63   13.353%   $221.7525   $221.75   $221.75   $221.80  
  Purchase #3 $111.36   3.352%   $115.0928   $115.09   $115.10   $115.10  
  Purchase #4 $156.43   5.412%   $164.896   $164.90   $164.90   $164.90  
  Purchase #5 $234.42   13.832%   $266.845   $266.85   $266.85   $266.80  
  Purchase #6 $42.98   12.644%   $48.4144   $48.41   $48.40   $48.40  
  Purchase #7 $207.68   8.439%   $225.2061   $225.21   $225.20   $225.20  
  7 purchase totals = $985.27       $1,083.5116   $1,083.51   $1,083.50   $1,083.50