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	$204.69	10.500%	$226.1825	$226.18	$226.20	$226.20
Purchase #2	$65.42	7.359%	$70.2343	$70.23	$70.25	$70.20
Purchase #3	$88.42	7.252%	$94.8322	$94.83	$94.85	$94.80
Purchase #4	$203.32	9.260%	$222.1474	$222.15	$222.15	$222.10
Purchase #5	$249.46	3.478%	$258.1362	$258.14	$258.15	$258.10
Purchase #6	$91.57	8.502%	$99.3553	$99.36	$99.35	$99.40
Purchase #7	$122.73	4.832%	$128.6603	$128.66	$128.65	$128.70
7 purchase totals =	$1,025.61		$1,099.5482	$1,099.55	$1,099.60	$1,099.50