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 $216.34   13.388%   $245.3036   $245.30   $245.30   $245.30  
  Purchase #2 $221.61   12.318%   $248.9079   $248.91   $248.90   $248.90  
  Purchase #3 $20.72   13.456%   $23.5081   $23.51   $23.50   $23.50  
  Purchase #4 $244.42   9.572%   $267.8159   $267.82   $267.80   $267.80  
  Purchase #5 $226.44   12.806%   $255.4379   $255.44   $255.45   $255.40  
  Purchase #6 $60.92   8.845%   $66.3084   $66.31   $66.30   $66.30  
  Purchase #7 $136.55   8.433%   $148.0653   $148.07   $148.05   $148.10  
  7 purchase totals = $1,127.00       $1,255.3471   $1,255.36   $1,255.30   $1,255.30