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	$40.68	4.223%	$42.3979	$42.40	$42.40	$42.40
Purchase #2	$72.58	7.439%	$77.9792	$77.98	$78.00	$78.00
Purchase #3	$66.82	13.231%	$75.661	$75.66	$75.65	$75.70
Purchase #4	$68.75	4.476%	$71.8273	$71.83	$71.85	$71.80
Purchase #5	$235.54	6.552%	$250.9726	$250.97	$250.95	$251.00
Purchase #6	$13.50	13.647%	$15.3423	$15.34	$15.35	$15.30
Purchase #7	$29.71	10.657%	$32.8762	$32.88	$32.90	$32.90
7 purchase totals =	$527.58		$567.0565	$567.06	$567.10	$567.10