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	$21.96	12.559%	$24.718	$24.72	$24.70	$24.70
Purchase #2	$84.82	5.862%	$89.7921	$89.79	$89.80	$89.80
Purchase #3	$234.82	12.331%	$263.7757	$263.78	$263.80	$263.80
Purchase #4	$188.56	4.339%	$196.7416	$196.74	$196.75	$196.70
Purchase #5	$66.41	4.341%	$69.2929	$69.29	$69.30	$69.30
Purchase #6	$77.82	4.725%	$81.497	$81.50	$81.50	$81.50
Purchase #7	$157.89	12.522%	$177.661	$177.66	$177.65	$177.70
7 purchase totals =	$832.28		$903.4783	$903.48	$903.50	$903.50