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	$140.56	6.834%	$150.1659	$150.17	$150.15	$150.20
Purchase #2	$159.54	4.750%	$167.1182	$167.12	$167.10	$167.10
Purchase #3	$44.70	13.561%	$50.7618	$50.76	$50.75	$50.80
Purchase #4	$140.79	3.574%	$145.8218	$145.82	$145.80	$145.80
Purchase #5	$94.89	3.345%	$98.0641	$98.06	$98.05	$98.10
Purchase #6	$250.94	10.205%	$276.5484	$276.55	$276.55	$276.50
Purchase #7	$108.49	5.356%	$114.3007	$114.30	$114.30	$114.30
7 purchase totals =	$939.91		$1,002.7809	$1,002.78	$1,002.70	$1,002.80