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 $61.25   6.269%   $65.0898   $65.09   $65.10   $65.10  
  Purchase #2 $12.64   12.696%   $14.2448   $14.24   $14.25   $14.20  
  Purchase #3 $58.74   3.553%   $60.827   $60.83   $60.85   $60.80  
  Purchase #4 $39.70   7.426%   $42.6481   $42.65   $42.65   $42.60  
  Purchase #5 $91.78   5.539%   $96.8637   $96.86   $96.85   $96.90  
  Purchase #6 $68.26   13.313%   $77.3475   $77.35   $77.35   $77.30  
  Purchase #7 $164.98   6.237%   $175.2698   $175.27   $175.25   $175.30  
  7 purchase totals = $497.35       $532.2907   $532.29   $532.30   $532.20