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	$5.73	7.568%	$6.1636	$6.16	$6.15	$6.20
Purchase #2	$97.33	12.530%	$109.5254	$109.53	$109.55	$109.50
Purchase #3	$135.28	6.624%	$144.2409	$144.24	$144.25	$144.20
Purchase #4	$153.39	3.379%	$158.573	$158.57	$158.55	$158.60
Purchase #5	$204.39	5.162%	$214.9406	$214.94	$214.95	$214.90
Purchase #6	$71.92	6.507%	$76.5998	$76.60	$76.60	$76.60
Purchase #7	$90.36	5.801%	$95.6018	$95.60	$95.60	$95.60
7 purchase totals =	$758.40		$805.6451	$805.64	$805.65	$805.60