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	$209.92	11.751%	$234.5877	$234.59	$234.60	$234.60
Purchase #2	$124.89	13.827%	$142.1585	$142.16	$142.15	$142.20
Purchase #3	$87.63	10.384%	$96.7295	$96.73	$96.75	$96.70
Purchase #4	$148.37	11.523%	$165.4667	$165.47	$165.45	$165.50
Purchase #5	$131.72	10.563%	$145.6336	$145.63	$145.65	$145.60
Purchase #6	$84.27	10.148%	$92.8217	$92.82	$92.80	$92.80
Purchase #7	$96.84	8.749%	$105.3125	$105.31	$105.30	$105.30
7 purchase totals =	$883.64		$982.7102	$982.71	$982.70	$982.70