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 $248.92   5.772%   $263.2877   $263.29   $263.30   $263.30  
  Purchase #2 $182.98   4.121%   $190.5206   $190.52   $190.50   $190.50  
  Purchase #3 $141.54   13.106%   $160.0902   $160.09   $160.10   $160.10  
  Purchase #4 $121.58   12.135%   $136.3337   $136.33   $136.35   $136.30  
  Purchase #5 $229.28   5.345%   $241.535   $241.54   $241.55   $241.50  
  Purchase #6 $111.30   10.407%   $122.883   $122.88   $122.90   $122.90  
  Purchase #7 $116.28   12.468%   $130.7778   $130.78   $130.80   $130.80  
  7 purchase totals = $1,151.88       $1,245.4280   $1,245.43   $1,245.50   $1,245.40