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	$169.42	11.491%	$188.8881	$188.89	$188.90	$188.90
Purchase #2	$72.69	6.205%	$77.2004	$77.20	$77.20	$77.20
Purchase #3	$238.72	3.605%	$247.3259	$247.33	$247.35	$247.30
Purchase #4	$155.32	8.742%	$168.8981	$168.90	$168.90	$168.90
Purchase #5	$114.30	12.142%	$128.1783	$128.18	$128.20	$128.20
Purchase #6	$29.95	5.861%	$31.7054	$31.71	$31.70	$31.70
Purchase #7	$113.91	4.110%	$118.5917	$118.59	$118.60	$118.60
7 purchase totals =	$894.31		$960.7879	$960.80	$960.85	$960.80