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	$248.74	10.722%	$275.4099	$275.41	$275.40	$275.40
Purchase #2	$206.57	5.827%	$218.6068	$218.61	$218.60	$218.60
Purchase #3	$105.84	13.192%	$119.8024	$119.80	$119.80	$119.80
Purchase #4	$53.54	7.664%	$57.6433	$57.64	$57.65	$57.60
Purchase #5	$29.29	12.109%	$32.8367	$32.84	$32.85	$32.80
Purchase #6	$148.30	7.596%	$159.5649	$159.56	$159.55	$159.60
Purchase #7	$108.57	7.665%	$116.8919	$116.89	$116.90	$116.90
7 purchase totals =	$900.85		$980.7559	$980.75	$980.75	$980.70