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 $82.77   4.746%   $86.6983   $86.70   $86.70   $86.70  
  Purchase #2 $241.92   11.295%   $269.2449   $269.24   $269.25   $269.20  
  Purchase #3 $184.63   5.623%   $195.0117   $195.01   $195.00   $195.00  
  Purchase #4 $60.95   6.363%   $64.8282   $64.83   $64.85   $64.80  
  Purchase #5 $40.88   9.735%   $44.8597   $44.86   $44.85   $44.90  
  Purchase #6 $190.40   12.798%   $214.7674   $214.77   $214.75   $214.80  
  Purchase #7 $21.88   9.548%   $23.9691   $23.97   $23.95   $24.00  
  7 purchase totals = $823.43       $899.3793   $899.38   $899.35   $899.40