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	$128.70	11.242%	$143.1685	$143.17	$143.15	$143.20
Purchase #2	$175.79	8.447%	$190.639	$190.64	$190.65	$190.60
Purchase #3	$229.73	5.480%	$242.3192	$242.32	$242.30	$242.30
Purchase #4	$25.68	7.691%	$27.655	$27.66	$27.65	$27.70
Purchase #5	$92.86	13.760%	$105.6375	$105.64	$105.65	$105.60
Purchase #6	$73.56	12.578%	$82.8124	$82.81	$82.80	$82.80
Purchase #7	$87.89	4.482%	$91.8292	$91.83	$91.85	$91.80
7 purchase totals =	$814.21		$884.0608	$884.07	$884.05	$884.00