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	$40.63	4.344%	$42.395	$42.40	$42.40	$42.40
Purchase #2	$143.65	8.767%	$156.2438	$156.24	$156.25	$156.20
Purchase #3	$46.49	9.811%	$51.0511	$51.05	$51.05	$51.10
Purchase #4	$50.42	11.259%	$56.0968	$56.10	$56.10	$56.10
Purchase #5	$168.46	6.335%	$179.1319	$179.13	$179.15	$179.10
Purchase #6	$92.95	11.115%	$103.2814	$103.28	$103.30	$103.30
Purchase #7	$134.97	8.460%	$146.3885	$146.39	$146.40	$146.40
7 purchase totals =	$677.57		$734.5885	$734.59	$734.65	$734.60