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	$97.75	12.292%	$109.7654	$109.77	$109.75	$109.80
Purchase #2	$56.78	6.488%	$60.4639	$60.46	$60.45	$60.50
Purchase #3	$177.88	3.816%	$184.6679	$184.67	$184.65	$184.70
Purchase #4	$13.34	7.648%	$14.3602	$14.36	$14.35	$14.40
Purchase #5	$52.59	10.408%	$58.0636	$58.06	$58.05	$58.10
Purchase #6	$167.42	7.194%	$179.4642	$179.46	$179.45	$179.50
Purchase #7	$75.64	9.586%	$82.8909	$82.89	$82.90	$82.90
7 purchase totals =	$641.40		$689.6761	$689.67	$689.60	$689.90