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 $240.35   5.598%   $253.8048   $253.80   $253.80   $253.80  
  Purchase #2 $120.54   4.804%   $126.3307   $126.33   $126.35   $126.30  
  Purchase #3 $226.54   5.530%   $239.0677   $239.07   $239.05   $239.10  
  Purchase #4 $241.95   10.717%   $267.8798   $267.88   $267.90   $267.90  
  Purchase #5 $10.90   11.284%   $12.13   $12.13   $12.15   $12.10  
  Purchase #6 $236.60   7.450%   $254.2267   $254.23   $254.25   $254.20  
  Purchase #7 $235.35   12.643%   $265.1053   $265.11   $265.10   $265.10  
  7 purchase totals = $1,312.23       $1,418.5450   $1,418.55   $1,418.60   $1,418.50