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	$20.91	10.292%	$23.0621	$23.06	$23.05	$23.10
Purchase #2	$6.41	12.154%	$7.1891	$7.19	$7.20	$7.20
Purchase #3	$209.30	4.603%	$218.9341	$218.93	$218.95	$218.90
Purchase #4	$24.85	13.757%	$28.2686	$28.27	$28.25	$28.30
Purchase #5	$190.40	3.251%	$196.5899	$196.59	$196.60	$196.60
Purchase #6	$155.31	6.850%	$165.9487	$165.95	$165.95	$165.90
Purchase #7	$179.27	6.355%	$190.6626	$190.66	$190.65	$190.70
7 purchase totals =	$786.45		$830.6551	$830.65	$830.65	$830.70