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 $53.77   13.469%   $61.0123   $61.01   $61.00   $61.00  
  Purchase #2 $101.53   10.303%   $111.9906   $111.99   $112.00   $112.00  
  Purchase #3 $153.44   3.872%   $159.3812   $159.38   $159.40   $159.40  
  Purchase #4 $195.37   13.583%   $221.9071   $221.91   $221.90   $221.90  
  Purchase #5 $92.99   3.576%   $96.3153   $96.32   $96.30   $96.30  
  Purchase #6 $88.65   12.714%   $99.921   $99.92   $99.90   $99.90  
  Purchase #7 $136.73   8.717%   $148.6488   $148.65   $148.65   $148.60  
  7 purchase totals = $822.48       $899.1763   $899.18   $899.15   $899.10