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 $207.38   12.293%   $232.8732   $232.87   $232.85   $232.90  
  Purchase #2 $167.38   4.624%   $175.1197   $175.12   $175.10   $175.10  
  Purchase #3 $164.29   11.167%   $182.6363   $182.64   $182.65   $182.60  
  Purchase #4 $143.36   13.254%   $162.3609   $162.36   $162.35   $162.40  
  Purchase #5 $26.65   13.480%   $30.2424   $30.24   $30.25   $30.20  
  Purchase #6 $249.43   4.610%   $260.9287   $260.93   $260.95   $260.90  
  Purchase #7 $66.32   7.493%   $71.2894   $71.29   $71.30   $71.30  
  7 purchase totals = $1,024.81       $1,115.4506   $1,115.45   $1,115.45   $1,115.40