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	$250.92	7.329%	$269.3099	$269.31	$269.30	$269.30
Purchase #2	$200.34	11.253%	$222.8843	$222.88	$222.90	$222.90
Purchase #3	$59.51	10.181%	$65.5687	$65.57	$65.55	$65.60
Purchase #4	$246.65	11.542%	$275.1183	$275.12	$275.10	$275.10
Purchase #5	$123.72	8.363%	$134.0667	$134.07	$134.05	$134.10
Purchase #6	$77.93	5.381%	$82.1234	$82.12	$82.10	$82.10
Purchase #7	$5.85	12.325%	$6.571	$6.57	$6.55	$6.60
7 purchase totals =	$964.92		$1,055.6423	$1,055.64	$1,055.55	$1,055.70