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 $217.40   13.862%   $247.536   $247.54   $247.55   $247.50  
  Purchase #2 $69.28   8.161%   $74.9339   $74.93   $74.95   $74.90  
  Purchase #3 $41.70   9.420%   $45.6281   $45.63   $45.65   $45.60  
  Purchase #4 $211.52   13.594%   $240.274   $240.27   $240.25   $240.30  
  Purchase #5 $243.71   4.614%   $254.9548   $254.95   $254.95   $255.00  
  Purchase #6 $193.72   3.433%   $200.3704   $200.37   $200.35   $200.40  
  Purchase #7 $9.76   12.142%   $10.9451   $10.95   $10.95   $10.90  
  7 purchase totals = $987.09       $1,074.6423   $1,074.64   $1,074.65   $1,074.60