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 $60.34   9.830%   $66.2714   $66.27   $66.25   $66.30  
  Purchase #2 $25.87   13.130%   $29.2667   $29.27   $29.25   $29.30  
  Purchase #3 $15.26   12.488%   $17.1657   $17.17   $17.15   $17.20  
  Purchase #4 $154.59   13.773%   $175.8817   $175.88   $175.90   $175.90  
  Purchase #5 $201.93   3.391%   $208.7774   $208.78   $208.80   $208.80  
  Purchase #6 $224.62   4.667%   $235.103   $235.10   $235.10   $235.10  
  Purchase #7 $203.66   13.835%   $231.8364   $231.84   $231.85   $231.80  
  7 purchase totals = $886.27       $964.3023   $964.31   $964.30   $964.40