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	$34.50	8.709%	$37.5046	$37.50	$37.50	$37.50
Purchase #2	$141.44	7.862%	$152.56	$152.56	$152.55	$152.60
Purchase #3	$56.45	6.211%	$59.9561	$59.96	$59.95	$60.00
Purchase #4	$228.95	13.236%	$259.2538	$259.25	$259.25	$259.30
Purchase #5	$130.81	3.118%	$134.8887	$134.89	$134.90	$134.90
Purchase #6	$213.76	11.144%	$237.5814	$237.58	$237.60	$237.60
Purchase #7	$115.54	13.740%	$131.4152	$131.42	$131.40	$131.40
7 purchase totals =	$921.45		$1,013.1598	$1,013.16	$1,013.15	$1,013.30