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	$171.28	9.701%	$187.8959	$187.90	$187.90	$187.90
Purchase #2	$127.99	8.485%	$138.85	$138.85	$138.85	$138.90
Purchase #3	$73.89	5.785%	$78.1645	$78.16	$78.15	$78.20
Purchase #4	$91.92	8.432%	$99.6707	$99.67	$99.65	$99.70
Purchase #5	$111.61	7.573%	$120.0622	$120.06	$120.05	$120.10
Purchase #6	$116.43	11.275%	$129.5575	$129.56	$129.55	$129.60
Purchase #7	$51.38	9.235%	$56.1249	$56.12	$56.10	$56.10
7 purchase totals =	$744.50		$810.3257	$810.32	$810.25	$810.50