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	$22.89	6.141%	$24.2957	$24.30	$24.30	$24.30
Purchase #2	$156.87	6.735%	$167.4352	$167.44	$167.45	$167.40
Purchase #3	$146.82	3.387%	$151.7928	$151.79	$151.80	$151.80
Purchase #4	$232.89	5.368%	$245.3915	$245.39	$245.40	$245.40
Purchase #5	$165.58	4.449%	$172.9467	$172.95	$172.95	$172.90
Purchase #6	$33.66	6.171%	$35.7372	$35.74	$35.75	$35.70
Purchase #7	$41.38	4.530%	$43.2545	$43.25	$43.25	$43.30
7 purchase totals =	$800.09		$840.8536	$840.86	$840.90	$840.80