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	$80.52	6.366%	$85.6459	$85.65	$85.65	$85.60
Purchase #2	$46.28	12.466%	$52.0493	$52.05	$52.05	$52.00
Purchase #3	$205.50	5.741%	$217.2978	$217.30	$217.30	$217.30
Purchase #4	$123.52	8.261%	$133.724	$133.72	$133.70	$133.70
Purchase #5	$64.62	11.479%	$72.0377	$72.04	$72.05	$72.00
Purchase #6	$9.89	13.511%	$11.2262	$11.23	$11.25	$11.20
Purchase #7	$93.41	6.755%	$99.7198	$99.72	$99.70	$99.70
7 purchase totals =	$623.74		$671.7007	$671.71	$671.70	$671.50