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	$72.55	10.441%	$80.1249	$80.12	$80.10	$80.10
Purchase #2	$116.78	9.134%	$127.4467	$127.45	$127.45	$127.40
Purchase #3	$103.72	5.472%	$109.3956	$109.40	$109.40	$109.40
Purchase #4	$52.43	11.411%	$58.4128	$58.41	$58.40	$58.40
Purchase #5	$45.97	4.843%	$48.1963	$48.20	$48.20	$48.20
Purchase #6	$221.45	5.640%	$233.9398	$233.94	$233.95	$233.90
Purchase #7	$61.61	12.731%	$69.4536	$69.45	$69.45	$69.50
7 purchase totals =	$674.51		$726.9697	$726.97	$726.95	$726.90