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	$243.91	8.426%	$264.4619	$264.46	$264.45	$264.50
Purchase #2	$81.72	13.345%	$92.6255	$92.63	$92.65	$92.60
Purchase #3	$105.96	9.723%	$116.2625	$116.26	$116.25	$116.30
Purchase #4	$51.91	10.849%	$57.5417	$57.54	$57.55	$57.50
Purchase #5	$9.80	3.659%	$10.1586	$10.16	$10.15	$10.20
Purchase #6	$222.28	7.484%	$238.9154	$238.92	$238.90	$238.90
Purchase #7	$51.64	11.760%	$57.7129	$57.71	$57.70	$57.70
7 purchase totals =	$767.22		$837.6785	$837.68	$837.65	$837.70