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	$132.72	13.565%	$150.7235	$150.72	$150.70	$150.70
Purchase #2	$248.48	4.128%	$258.7373	$258.74	$258.75	$258.70
Purchase #3	$89.28	4.199%	$93.0289	$93.03	$93.05	$93.00
Purchase #4	$175.40	8.599%	$190.4826	$190.48	$190.50	$190.50
Purchase #5	$113.52	12.686%	$127.9211	$127.92	$127.90	$127.90
Purchase #6	$20.40	9.665%	$22.3717	$22.37	$22.35	$22.40
Purchase #7	$126.59	7.787%	$136.4476	$136.45	$136.45	$136.40
7 purchase totals =	$906.39		$979.7127	$979.71	$979.70	$979.60