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 $55.68   8.524%   $60.4262   $60.43   $60.45   $60.40  
  Purchase #2 $184.34   3.440%   $190.6813   $190.68   $190.70   $190.70  
  Purchase #3 $64.62   8.369%   $70.028   $70.03   $70.05   $70.00  
  Purchase #4 $10.35   5.150%   $10.883   $10.88   $10.90   $10.90  
  Purchase #5 $203.43   8.780%   $221.2912   $221.29   $221.30   $221.30  
  Purchase #6 $58.54   4.407%   $61.1199   $61.12   $61.10   $61.10  
  Purchase #7 $229.63   10.395%   $253.5   $253.50   $253.50   $253.50  
  7 purchase totals = $806.59       $867.9296   $867.93   $868.00   $867.90