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 $240.52   13.497%   $272.983   $272.98   $273.00   $273.00  
  Purchase #2 $28.48   4.181%   $29.6707   $29.67   $29.65   $29.70  
  Purchase #3 $244.27   11.335%   $271.958   $271.96   $271.95   $272.00  
  Purchase #4 $217.85   3.853%   $226.2438   $226.24   $226.25   $226.20  
  Purchase #5 $220.60   5.848%   $233.5007   $233.50   $233.50   $233.50  
  Purchase #6 $126.53   11.491%   $141.0696   $141.07   $141.05   $141.10  
  Purchase #7 $247.43   7.162%   $265.1509   $265.15   $265.15   $265.20  
  7 purchase totals = $1,325.68       $1,440.5767   $1,440.57   $1,440.55   $1,440.70