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	$93.35	7.670%	$100.5099	$100.51	$100.50	$100.50
Purchase #2	$80.68	11.520%	$89.9743	$89.97	$89.95	$90.00
Purchase #3	$89.88	7.275%	$96.4188	$96.42	$96.40	$96.40
Purchase #4	$93.36	6.811%	$99.7187	$99.72	$99.70	$99.70
Purchase #5	$50.29	12.476%	$56.5642	$56.56	$56.55	$56.60
Purchase #6	$139.28	5.190%	$146.5086	$146.51	$146.50	$146.50
Purchase #7	$195.33	10.257%	$215.365	$215.37	$215.35	$215.40
7 purchase totals =	$742.17		$805.0595	$805.06	$804.95	$805.10