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	$176.47	7.204%	$189.1829	$189.18	$189.20	$189.20
Purchase #2	$148.50	6.874%	$158.7079	$158.71	$158.70	$158.70
Purchase #3	$223.40	6.728%	$238.4304	$238.43	$238.45	$238.40
Purchase #4	$47.45	8.251%	$51.3651	$51.37	$51.35	$51.40
Purchase #5	$78.85	5.167%	$82.9242	$82.92	$82.90	$82.90
Purchase #6	$246.83	10.405%	$272.5127	$272.51	$272.50	$272.50
Purchase #7	$220.53	4.869%	$231.2676	$231.27	$231.25	$231.30
7 purchase totals =	$1,142.03		$1,224.3908	$1,224.39	$1,224.35	$1,224.40