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	$120.95	8.567%	$131.3118	$131.31	$131.30	$131.30
Purchase #2	$130.42	3.569%	$135.0747	$135.07	$135.05	$135.10
Purchase #3	$219.95	6.323%	$233.8574	$233.86	$233.85	$233.90
Purchase #4	$72.63	13.414%	$82.3726	$82.37	$82.35	$82.40
Purchase #5	$105.79	3.776%	$109.7846	$109.78	$109.80	$109.80
Purchase #6	$242.94	4.412%	$253.6585	$253.66	$253.65	$253.70
Purchase #7	$18.63	11.154%	$20.708	$20.71	$20.70	$20.70
7 purchase totals =	$911.31		$966.7676	$966.76	$966.70	$966.90