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	$232.40	3.729%	$241.0662	$241.07	$241.05	$241.10
Purchase #2	$124.40	13.140%	$140.7462	$140.75	$140.75	$140.70
Purchase #3	$54.62	5.225%	$57.4739	$57.47	$57.45	$57.50
Purchase #4	$127.67	13.810%	$145.3012	$145.30	$145.30	$145.30
Purchase #5	$122.50	3.693%	$127.0239	$127.02	$127.00	$127.00
Purchase #6	$156.83	7.718%	$168.9341	$168.93	$168.95	$168.90
Purchase #7	$75.28	10.133%	$82.9081	$82.91	$82.90	$82.90
7 purchase totals =	$893.70		$963.4536	$963.45	$963.40	$963.40