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 $66.44   10.352%   $73.3179   $73.32   $73.30   $73.30  
  Purchase #2 $99.95   10.302%   $110.2468   $110.25   $110.25   $110.20  
  Purchase #3 $215.66   4.834%   $226.085   $226.09   $226.10   $226.10  
  Purchase #4 $94.89   4.427%   $99.0908   $99.09   $99.10   $99.10  
  Purchase #5 $206.58   7.106%   $221.2596   $221.26   $221.25   $221.30  
  Purchase #6 $72.49   5.336%   $76.3581   $76.36   $76.35   $76.40  
  Purchase #7 $136.44   13.713%   $155.15   $155.15   $155.15   $155.20  
  7 purchase totals = $892.45       $961.5082   $961.52   $961.50   $961.60