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	$40.36	5.284%	$42.4926	$42.49	$42.50	$42.50
Purchase #2	$154.81	11.206%	$172.158	$172.16	$172.15	$172.20
Purchase #3	$176.92	9.604%	$193.9114	$193.91	$193.90	$193.90
Purchase #4	$52.33	6.486%	$55.7241	$55.72	$55.70	$55.70
Purchase #5	$26.34	11.768%	$29.4397	$29.44	$29.45	$29.40
Purchase #6	$92.67	9.146%	$101.1456	$101.15	$101.15	$101.10
Purchase #7	$175.39	8.265%	$189.886	$189.89	$189.90	$189.90
7 purchase totals =	$718.82		$784.7574	$784.76	$784.75	$784.70