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 $249.92   12.678%   $281.6049   $281.60   $281.60   $281.60  
  Purchase #2 $38.48   12.860%   $43.4285   $43.43   $43.45   $43.40  
  Purchase #3 $60.33   8.452%   $65.4291   $65.43   $65.45   $65.40  
  Purchase #4 $78.89   6.674%   $84.1551   $84.16   $84.15   $84.20  
  Purchase #5 $233.97   8.813%   $254.5898   $254.59   $254.60   $254.60  
  Purchase #6 $224.69   12.643%   $253.0976   $253.10   $253.10   $253.10  
  Purchase #7 $62.63   13.301%   $70.9604   $70.96   $70.95   $71.00  
  7 purchase totals = $948.91       $1,053.2654   $1,053.27   $1,053.30   $1,053.30