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	$87.51	13.301%	$99.1497	$99.15	$99.15	$99.10
Purchase #2	$108.32	4.637%	$113.3428	$113.34	$113.35	$113.30
Purchase #3	$173.32	10.713%	$191.8878	$191.89	$191.90	$191.90
Purchase #4	$92.35	4.441%	$96.4513	$96.45	$96.45	$96.50
Purchase #5	$197.86	8.546%	$214.7691	$214.77	$214.75	$214.80
Purchase #6	$206.82	10.404%	$228.3376	$228.34	$228.35	$228.30
Purchase #7	$81.54	12.536%	$91.7619	$91.76	$91.75	$91.80
7 purchase totals =	$947.72		$1,035.7002	$1,035.70	$1,035.70	$1,035.70