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	$115.73	12.771%	$130.5099	$130.51	$130.50	$130.50
Purchase #2	$34.84	12.676%	$39.2563	$39.26	$39.25	$39.30
Purchase #3	$146.76	11.841%	$164.1379	$164.14	$164.15	$164.10
Purchase #4	$118.50	7.833%	$127.7821	$127.78	$127.80	$127.80
Purchase #5	$152.85	3.675%	$158.4672	$158.47	$158.45	$158.50
Purchase #6	$188.39	8.644%	$204.6744	$204.67	$204.65	$204.70
Purchase #7	$110.50	4.349%	$115.3056	$115.31	$115.30	$115.30
7 purchase totals =	$867.57		$940.1334	$940.14	$940.10	$940.20