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 $95.65   11.638%   $106.7817   $106.78   $106.80   $106.80  
  Purchase #2 $193.86   11.246%   $215.6615   $215.66   $215.65   $215.70  
  Purchase #3 $159.39   3.179%   $164.457   $164.46   $164.45   $164.50  
  Purchase #4 $113.53   11.219%   $126.2669   $126.27   $126.25   $126.30  
  Purchase #5 $38.38   11.707%   $42.8731   $42.87   $42.85   $42.90  
  Purchase #6 $84.68   3.495%   $87.6396   $87.64   $87.65   $87.60  
  Purchase #7 $167.99   8.541%   $182.338   $182.34   $182.35   $182.30  
  7 purchase totals = $853.48       $926.0178   $926.02   $926.00   $926.10