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	$228.32	10.110%	$251.4032	$251.40	$251.40	$251.40
Purchase #2	$212.29	7.227%	$227.6322	$227.63	$227.65	$227.60
Purchase #3	$173.93	9.728%	$190.8499	$190.85	$190.85	$190.80
Purchase #4	$78.64	8.188%	$85.079	$85.08	$85.10	$85.10
Purchase #5	$96.88	11.327%	$107.8536	$107.85	$107.85	$107.90
Purchase #6	$26.84	11.435%	$29.9092	$29.91	$29.90	$29.90
Purchase #7	$108.37	3.280%	$111.9245	$111.92	$111.90	$111.90
7 purchase totals =	$925.27		$1,004.6516	$1,004.64	$1,004.65	$1,004.60