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 $97.53   4.214%   $101.6399   $101.64   $101.65   $101.60  
  Purchase #2 $216.29   6.806%   $231.0107   $231.01   $231.00   $231.00  
  Purchase #3 $151.26   12.747%   $170.5411   $170.54   $170.55   $170.50  
  Purchase #4 $245.64   7.438%   $263.9107   $263.91   $263.90   $263.90  
  Purchase #5 $202.77   6.164%   $215.2687   $215.27   $215.25   $215.30  
  Purchase #6 $98.81   9.195%   $107.8956   $107.90   $107.90   $107.90  
  Purchase #7 $79.95   8.696%   $86.9025   $86.90   $86.90   $86.90  
  7 purchase totals = $1,092.25       $1,177.1692   $1,177.17   $1,177.15   $1,177.10