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	$49.48	9.504%	$54.1826	$54.18	$54.20	$54.20
Purchase #2	$222.64	7.216%	$238.7057	$238.71	$238.70	$238.70
Purchase #3	$41.40	13.211%	$46.8694	$46.87	$46.85	$46.90
Purchase #4	$211.60	10.175%	$233.1303	$233.13	$233.15	$233.10
Purchase #5	$78.69	6.207%	$83.5743	$83.57	$83.55	$83.60
Purchase #6	$173.54	4.219%	$180.8617	$180.86	$180.85	$180.90
Purchase #7	$51.54	8.358%	$55.8477	$55.85	$55.85	$55.80
7 purchase totals =	$828.89		$893.1717	$893.17	$893.15	$893.20