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	$157.37	4.393%	$164.2833	$164.28	$164.30	$164.30
Purchase #2	$198.32	6.211%	$210.6377	$210.64	$210.65	$210.60
Purchase #3	$152.75	4.420%	$159.5016	$159.50	$159.50	$159.50
Purchase #4	$151.83	8.830%	$165.2366	$165.24	$165.25	$165.20
Purchase #5	$84.86	7.692%	$91.3874	$91.39	$91.40	$91.40
Purchase #6	$88.49	3.553%	$91.634	$91.63	$91.65	$91.60
Purchase #7	$183.81	13.330%	$208.3119	$208.31	$208.30	$208.30
7 purchase totals =	$1,017.43		$1,090.9925	$1,090.99	$1,091.05	$1,090.90