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	$37.39	5.451%	$39.4281	$39.43	$39.45	$39.40
Purchase #2	$120.58	13.377%	$136.71	$136.71	$136.70	$136.70
Purchase #3	$130.30	7.389%	$139.9279	$139.93	$139.95	$139.90
Purchase #4	$126.81	3.529%	$131.2851	$131.29	$131.30	$131.30
Purchase #5	$120.84	10.206%	$133.1729	$133.17	$133.15	$133.20
Purchase #6	$211.33	5.346%	$222.6277	$222.63	$222.65	$222.60
Purchase #7	$156.88	9.152%	$171.2377	$171.24	$171.25	$171.20
7 purchase totals =	$904.13		$974.3894	$974.40	$974.45	$974.30