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	$29.26	13.193%	$33.1203	$33.12	$33.10	$33.10
Purchase #2	$158.86	4.185%	$165.5083	$165.51	$165.50	$165.50
Purchase #3	$97.90	5.305%	$103.0936	$103.09	$103.10	$103.10
Purchase #4	$130.56	12.734%	$147.1855	$147.19	$147.20	$147.20
Purchase #5	$193.76	3.453%	$200.4505	$200.45	$200.45	$200.50
Purchase #6	$164.52	4.394%	$171.749	$171.75	$171.75	$171.70
Purchase #7	$32.46	6.786%	$34.6627	$34.66	$34.65	$34.70
7 purchase totals =	$807.32		$855.7699	$855.77	$855.75	$855.80