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	$10.68	12.637%	$12.0296	$12.03	$12.05	$12.00
Purchase #2	$151.58	11.430%	$168.9056	$168.91	$168.90	$168.90
Purchase #3	$109.45	13.722%	$124.4687	$124.47	$124.45	$124.50
Purchase #4	$27.46	7.414%	$29.4959	$29.50	$29.50	$29.50
Purchase #5	$218.87	11.874%	$244.8586	$244.86	$244.85	$244.90
Purchase #6	$196.62	8.365%	$213.0673	$213.07	$213.05	$213.10
Purchase #7	$242.40	13.580%	$275.3179	$275.32	$275.30	$275.30
7 purchase totals =	$957.06		$1,068.1436	$1,068.16	$1,068.10	$1,068.20