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	$133.58	5.534%	$140.9723	$140.97	$140.95	$141.00
Purchase #2	$39.36	8.406%	$42.6686	$42.67	$42.65	$42.70
Purchase #3	$103.27	4.226%	$107.6342	$107.63	$107.65	$107.60
Purchase #4	$57.85	6.597%	$61.6664	$61.67	$61.65	$61.70
Purchase #5	$16.85	12.422%	$18.9431	$18.94	$18.95	$18.90
Purchase #6	$53.69	10.764%	$59.4692	$59.47	$59.45	$59.50
Purchase #7	$77.92	9.180%	$85.0731	$85.07	$85.05	$85.10
7 purchase totals =	$482.52		$516.4269	$516.42	$516.35	$516.50