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	$42.58	6.306%	$45.2651	$45.27	$45.25	$45.30
Purchase #2	$209.87	10.219%	$231.3166	$231.32	$231.30	$231.30
Purchase #3	$163.90	4.684%	$171.5771	$171.58	$171.60	$171.60
Purchase #4	$109.78	13.434%	$124.5278	$124.53	$124.55	$124.50
Purchase #5	$52.94	7.809%	$57.0741	$57.07	$57.05	$57.10
Purchase #6	$177.49	4.573%	$185.6066	$185.61	$185.60	$185.60
Purchase #7	$139.84	9.364%	$152.9346	$152.93	$152.95	$152.90
7 purchase totals =	$896.40		$968.3019	$968.31	$968.30	$968.30