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	$123.95	8.694%	$134.7262	$134.73	$134.75	$134.70
Purchase #2	$9.86	4.711%	$10.3245	$10.32	$10.30	$10.30
Purchase #3	$127.54	13.163%	$144.3281	$144.33	$144.35	$144.30
Purchase #4	$81.79	11.847%	$91.4797	$91.48	$91.50	$91.50
Purchase #5	$83.94	6.243%	$89.1804	$89.18	$89.20	$89.20
Purchase #6	$244.45	8.469%	$265.1525	$265.15	$265.15	$265.20
Purchase #7	$87.76	9.220%	$95.8515	$95.85	$95.85	$95.90
7 purchase totals =	$759.29		$831.0429	$831.04	$831.10	$831.10