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	$27.29	12.456%	$30.6892	$30.69	$30.70	$30.70
Purchase #2	$73.53	12.562%	$82.7668	$82.77	$82.75	$82.80
Purchase #3	$146.86	8.405%	$159.2036	$159.20	$159.20	$159.20
Purchase #4	$157.32	7.152%	$168.5715	$168.57	$168.55	$168.60
Purchase #5	$57.73	10.753%	$63.9377	$63.94	$63.95	$63.90
Purchase #6	$174.59	12.521%	$196.4504	$196.45	$196.45	$196.50
Purchase #7	$106.39	13.401%	$120.6473	$120.65	$120.65	$120.60
7 purchase totals =	$743.71		$822.2665	$822.27	$822.25	$822.30