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	$129.54	4.507%	$135.3784	$135.38	$135.40	$135.40
Purchase #2	$55.47	11.524%	$61.8624	$61.86	$61.85	$61.90
Purchase #3	$244.39	4.458%	$255.2849	$255.28	$255.30	$255.30
Purchase #4	$87.89	13.774%	$99.996	$100.00	$100.00	$100.00
Purchase #5	$241.40	7.513%	$259.5364	$259.54	$259.55	$259.50
Purchase #6	$34.29	9.422%	$37.5208	$37.52	$37.50	$37.50
Purchase #7	$243.55	4.390%	$254.2418	$254.24	$254.25	$254.20
7 purchase totals =	$1,036.53		$1,103.8207	$1,103.82	$1,103.85	$1,103.80