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	$122.70	10.323%	$135.3663	$135.37	$135.35	$135.40
Purchase #2	$60.66	7.798%	$65.3903	$65.39	$65.40	$65.40
Purchase #3	$29.52	13.302%	$33.4468	$33.45	$33.45	$33.40
Purchase #4	$130.82	7.256%	$140.3123	$140.31	$140.30	$140.30
Purchase #5	$157.37	10.225%	$173.4611	$173.46	$173.45	$173.50
Purchase #6	$126.70	11.654%	$141.4656	$141.47	$141.45	$141.50
Purchase #7	$118.69	10.739%	$131.4361	$131.44	$131.45	$131.40
7 purchase totals =	$746.46		$820.8785	$820.89	$820.85	$820.90