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	$55.40	6.542%	$59.0243	$59.02	$59.00	$59.00
Purchase #2	$241.35	13.657%	$274.3112	$274.31	$274.30	$274.30
Purchase #3	$152.74	13.570%	$173.4668	$173.47	$173.45	$173.50
Purchase #4	$225.94	5.497%	$238.3599	$238.36	$238.35	$238.40
Purchase #5	$88.83	4.192%	$92.5538	$92.55	$92.55	$92.60
Purchase #6	$57.36	7.754%	$61.8077	$61.81	$61.80	$61.80
Purchase #7	$126.54	3.240%	$130.6399	$130.64	$130.65	$130.60
7 purchase totals =	$948.16		$1,030.1636	$1,030.16	$1,030.10	$1,030.20