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 $81.63   5.343%   $85.9915   $85.99   $86.00   $86.00  
  Purchase #2 $40.97   7.700%   $44.1247   $44.12   $44.10   $44.10  
  Purchase #3 $113.59   4.622%   $118.8401   $118.84   $118.85   $118.80  
  Purchase #4 $212.35   4.398%   $221.6892   $221.69   $221.70   $221.70  
  Purchase #5 $82.95   11.534%   $92.5175   $92.52   $92.50   $92.50  
  Purchase #6 $209.75   3.309%   $216.6906   $216.69   $216.70   $216.70  
  Purchase #7 $58.99   5.204%   $62.0598   $62.06   $62.05   $62.10  
  7 purchase totals = $800.23       $841.9134   $841.91   $841.90   $841.90