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	$33.63	12.761%	$37.9215	$37.92	$37.90	$37.90
Purchase #2	$113.39	12.264%	$127.2961	$127.30	$127.30	$127.30
Purchase #3	$157.43	11.356%	$175.3078	$175.31	$175.30	$175.30
Purchase #4	$177.75	12.292%	$199.599	$199.60	$199.60	$199.60
Purchase #5	$30.96	7.721%	$33.3504	$33.35	$33.35	$33.40
Purchase #6	$161.52	7.601%	$173.7971	$173.80	$173.80	$173.80
Purchase #7	$101.32	11.281%	$112.7499	$112.75	$112.75	$112.70
7 purchase totals =	$776.00		$860.0218	$860.03	$860.00	$860.00