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	$179.51	8.399%	$194.587	$194.59	$194.60	$194.60
Purchase #2	$133.49	8.515%	$144.8567	$144.86	$144.85	$144.90
Purchase #3	$208.56	6.510%	$222.1373	$222.14	$222.15	$222.10
Purchase #4	$8.83	13.742%	$10.0434	$10.04	$10.05	$10.00
Purchase #5	$148.58	12.722%	$167.4823	$167.48	$167.50	$167.50
Purchase #6	$226.93	4.385%	$236.8809	$236.88	$236.90	$236.90
Purchase #7	$226.60	8.261%	$245.3194	$245.32	$245.30	$245.30
7 purchase totals =	$1,132.50		$1,221.3070	$1,221.31	$1,221.35	$1,221.30