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	$136.73	6.346%	$145.4069	$145.41	$145.40	$145.40
Purchase #2	$152.34	6.271%	$161.8932	$161.89	$161.90	$161.90
Purchase #3	$142.94	9.345%	$156.2977	$156.30	$156.30	$156.30
Purchase #4	$20.63	8.169%	$22.3153	$22.32	$22.30	$22.30
Purchase #5	$86.47	3.767%	$89.7273	$89.73	$89.75	$89.70
Purchase #6	$130.67	11.770%	$146.0499	$146.05	$146.05	$146.00
Purchase #7	$194.38	13.466%	$220.5552	$220.56	$220.55	$220.60
7 purchase totals =	$864.16		$942.2455	$942.26	$942.25	$942.20