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	$180.92	5.654%	$191.1492	$191.15	$191.15	$191.10
Purchase #2	$115.62	9.824%	$126.9785	$126.98	$127.00	$127.00
Purchase #3	$220.72	11.399%	$245.8799	$245.88	$245.90	$245.90
Purchase #4	$153.70	12.820%	$173.4043	$173.40	$173.40	$173.40
Purchase #5	$17.31	9.831%	$19.0117	$19.01	$19.00	$19.00
Purchase #6	$50.31	4.781%	$52.7153	$52.72	$52.70	$52.70
Purchase #7	$147.95	12.711%	$166.7559	$166.76	$166.75	$166.80
7 purchase totals =	$886.53		$975.8948	$975.90	$975.90	$975.90