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	$242.79	11.684%	$271.1576	$271.16	$271.15	$271.20
Purchase #2	$237.64	3.847%	$246.782	$246.78	$246.80	$246.80
Purchase #3	$239.65	6.267%	$254.6689	$254.67	$254.65	$254.70
Purchase #4	$131.98	11.834%	$147.5985	$147.60	$147.60	$147.60
Purchase #5	$51.96	10.619%	$57.4776	$57.48	$57.50	$57.50
Purchase #6	$157.89	6.772%	$168.5823	$168.58	$168.60	$168.60
Purchase #7	$159.59	3.547%	$165.2507	$165.25	$165.25	$165.30
7 purchase totals =	$1,221.50		$1,311.5176	$1,311.52	$1,311.55	$1,311.70