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 $68.41   8.165%   $73.9957   $74.00   $74.00   $74.00  
  Purchase #2 $229.90   4.114%   $239.3581   $239.36   $239.35   $239.40  
  Purchase #3 $143.89   3.119%   $148.3779   $148.38   $148.40   $148.40  
  Purchase #4 $103.98   7.874%   $112.1674   $112.17   $112.15   $112.20  
  Purchase #5 $85.99   11.799%   $96.136   $96.14   $96.15   $96.10  
  Purchase #6 $19.42   4.550%   $20.3036   $20.30   $20.30   $20.30  
  Purchase #7 $162.40   12.526%   $182.7422   $182.74   $182.75   $182.70  
  7 purchase totals = $813.99       $873.0809   $873.09   $873.10   $873.10