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	$138.40	13.674%	$157.3248	$157.32	$157.30	$157.30
Purchase #2	$74.54	13.807%	$84.8317	$84.83	$84.85	$84.80
Purchase #3	$68.41	4.410%	$71.4269	$71.43	$71.45	$71.40
Purchase #4	$99.45	3.788%	$103.2172	$103.22	$103.20	$103.20
Purchase #5	$107.25	10.740%	$118.7687	$118.77	$118.75	$118.80
Purchase #6	$97.89	7.721%	$105.4481	$105.45	$105.45	$105.40
Purchase #7	$180.41	13.788%	$205.2849	$205.28	$205.30	$205.30
7 purchase totals =	$766.35		$846.3023	$846.30	$846.30	$846.20