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 $84.96   13.214%   $96.1866   $96.19   $96.20   $96.20  
  Purchase #2 $68.95   4.214%   $71.8556   $71.86   $71.85   $71.90  
  Purchase #3 $147.63   5.846%   $156.2604   $156.26   $156.25   $156.30  
  Purchase #4 $248.75   4.267%   $259.3642   $259.36   $259.35   $259.40  
  Purchase #5 $229.67   10.758%   $254.3779   $254.38   $254.40   $254.40  
  Purchase #6 $176.25   3.309%   $182.0821   $182.08   $182.10   $182.10  
  Purchase #7 $153.64   11.215%   $170.8707   $170.87   $170.85   $170.90  
  7 purchase totals = $1,109.85       $1,190.9975   $1,191.00   $1,191.00   $1,191.20