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	$205.75	13.307%	$233.1292	$233.13	$233.15	$233.10
Purchase #2	$55.90	7.129%	$59.8851	$59.89	$59.90	$59.90
Purchase #3	$130.76	8.262%	$141.5634	$141.56	$141.55	$141.60
Purchase #4	$70.65	11.690%	$78.909	$78.91	$78.90	$78.90
Purchase #5	$123.75	9.792%	$135.8676	$135.87	$135.85	$135.90
Purchase #6	$8.69	5.193%	$9.1413	$9.14	$9.15	$9.10
Purchase #7	$110.81	4.479%	$115.7732	$115.77	$115.75	$115.80
7 purchase totals =	$706.31		$774.2688	$774.27	$774.25	$774.30