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	$40.64	4.298%	$42.3867	$42.39	$42.40	$42.40
Purchase #2	$156.35	12.741%	$176.2706	$176.27	$176.25	$176.30
Purchase #3	$138.89	4.784%	$145.5345	$145.53	$145.55	$145.50
Purchase #4	$136.70	10.343%	$150.8389	$150.84	$150.85	$150.80
Purchase #5	$73.28	12.108%	$82.1527	$82.15	$82.15	$82.20
Purchase #6	$64.82	7.146%	$69.452	$69.45	$69.45	$69.50
Purchase #7	$161.95	6.113%	$171.85	$171.85	$171.85	$171.90
7 purchase totals =	$772.63		$838.4854	$838.48	$838.50	$838.60