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	$229.60	12.760%	$258.897	$258.90	$258.90	$258.90
Purchase #2	$207.55	13.251%	$235.0525	$235.05	$235.05	$235.10
Purchase #3	$186.89	10.447%	$206.4144	$206.41	$206.40	$206.40
Purchase #4	$190.33	3.188%	$196.3977	$196.40	$196.40	$196.40
Purchase #5	$52.41	13.275%	$59.3674	$59.37	$59.35	$59.40
Purchase #6	$197.58	6.841%	$211.0964	$211.10	$211.10	$211.10
Purchase #7	$50.61	7.214%	$54.261	$54.26	$54.25	$54.30
7 purchase totals =	$1,114.97		$1,221.4864	$1,221.49	$1,221.45	$1,221.60