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 $59.56   12.442%   $66.9705   $66.97   $66.95   $67.00  
  Purchase #2 $55.52   9.784%   $60.9521   $60.95   $60.95   $61.00  
  Purchase #3 $213.55   13.386%   $242.1358   $242.14   $242.15   $242.10  
  Purchase #4 $15.47   5.170%   $16.2698   $16.27   $16.25   $16.30  
  Purchase #5 $249.25   5.206%   $262.226   $262.23   $262.25   $262.20  
  Purchase #6 $161.92   8.238%   $175.259   $175.26   $175.25   $175.30  
  Purchase #7 $100.29   4.254%   $104.5563   $104.56   $104.55   $104.60  
  7 purchase totals = $855.56       $928.3695   $928.38   $928.35   $928.50