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	$138.58	6.545%	$147.6501	$147.65	$147.65	$147.70
Purchase #2	$77.32	4.480%	$80.7839	$80.78	$80.80	$80.80
Purchase #3	$43.61	11.208%	$48.4978	$48.50	$48.50	$48.50
Purchase #4	$130.96	10.328%	$144.4855	$144.49	$144.50	$144.50
Purchase #5	$47.80	11.472%	$53.2836	$53.28	$53.30	$53.30
Purchase #6	$48.79	4.173%	$50.826	$50.83	$50.85	$50.80
Purchase #7	$82.75	6.708%	$88.3009	$88.30	$88.30	$88.30
7 purchase totals =	$569.81		$613.8278	$613.83	$613.90	$613.90