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	$70.26	11.769%	$78.5289	$78.53	$78.55	$78.50
Purchase #2	$172.50	8.732%	$187.5627	$187.56	$187.55	$187.60
Purchase #3	$173.74	8.648%	$188.765	$188.77	$188.75	$188.80
Purchase #4	$228.82	13.424%	$259.5368	$259.54	$259.55	$259.50
Purchase #5	$54.38	8.581%	$59.0463	$59.05	$59.05	$59.00
Purchase #6	$231.88	6.820%	$247.6942	$247.69	$247.70	$247.70
Purchase #7	$223.69	10.305%	$246.7413	$246.74	$246.75	$246.70
7 purchase totals =	$1,155.27		$1,267.8752	$1,267.88	$1,267.90	$1,267.80