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	$72.72	13.763%	$82.7285	$82.73	$82.75	$82.70
Purchase #2	$150.41	3.468%	$155.6262	$155.63	$155.65	$155.60
Purchase #3	$78.63	13.705%	$89.4062	$89.41	$89.40	$89.40
Purchase #4	$9.88	11.227%	$10.9892	$10.99	$11.00	$11.00
Purchase #5	$94.93	8.651%	$103.1424	$103.14	$103.15	$103.10
Purchase #6	$219.62	7.260%	$235.5644	$235.56	$235.55	$235.60
Purchase #7	$119.78	4.157%	$124.7593	$124.76	$124.75	$124.80
7 purchase totals =	$745.97		$802.2162	$802.22	$802.25	$802.20