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	$103.85	3.497%	$107.4816	$107.48	$107.50	$107.50
Purchase #2	$52.62	9.446%	$57.5905	$57.59	$57.60	$57.60
Purchase #3	$116.29	12.793%	$131.167	$131.17	$131.15	$131.20
Purchase #4	$135.26	4.822%	$141.7822	$141.78	$141.80	$141.80
Purchase #5	$28.46	13.632%	$32.3397	$32.34	$32.35	$32.30
Purchase #6	$22.81	3.114%	$23.5203	$23.52	$23.50	$23.50
Purchase #7	$115.41	4.748%	$120.8897	$120.89	$120.90	$120.90
7 purchase totals =	$574.70		$614.7710	$614.77	$614.80	$614.80