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	$36.62	10.783%	$40.5687	$40.57	$40.55	$40.60
Purchase #2	$50.34	11.519%	$56.1387	$56.14	$56.15	$56.10
Purchase #3	$67.85	6.196%	$72.054	$72.05	$72.05	$72.10
Purchase #4	$61.67	6.836%	$65.8858	$65.89	$65.90	$65.90
Purchase #5	$49.33	10.174%	$54.3488	$54.35	$54.35	$54.30
Purchase #6	$201.89	13.446%	$229.0361	$229.04	$229.05	$229.00
Purchase #7	$225.61	13.683%	$256.4802	$256.48	$256.50	$256.50
7 purchase totals =	$693.31		$774.5123	$774.52	$774.55	$774.50