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	$50.86	4.403%	$53.0994	$53.10	$53.10	$53.10
Purchase #2	$34.56	4.500%	$36.1152	$36.12	$36.10	$36.10
Purchase #3	$20.47	9.729%	$22.4615	$22.46	$22.45	$22.50
Purchase #4	$141.46	3.400%	$146.2696	$146.27	$146.25	$146.30
Purchase #5	$89.88	9.853%	$98.7359	$98.74	$98.75	$98.70
Purchase #6	$144.60	8.102%	$156.3155	$156.32	$156.30	$156.30
Purchase #7	$240.64	13.171%	$272.3347	$272.33	$272.35	$272.30
7 purchase totals =	$722.47		$785.3318	$785.34	$785.30	$785.30