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	$107.97	11.635%	$120.5323	$120.53	$120.55	$120.50
Purchase #2	$128.83	7.744%	$138.8066	$138.81	$138.80	$138.80
Purchase #3	$151.64	13.612%	$172.2812	$172.28	$172.30	$172.30
Purchase #4	$16.57	12.444%	$18.632	$18.63	$18.65	$18.60
Purchase #5	$80.78	11.178%	$89.8096	$89.81	$89.80	$89.80
Purchase #6	$78.87	12.427%	$88.6712	$88.67	$88.65	$88.70
Purchase #7	$90.32	10.794%	$100.0691	$100.07	$100.05	$100.10
7 purchase totals =	$654.98		$728.8020	$728.80	$728.80	$728.80