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	$233.25	8.445%	$252.948	$252.95	$252.95	$252.90
Purchase #2	$99.58	3.275%	$102.8412	$102.84	$102.85	$102.80
Purchase #3	$36.59	7.795%	$39.4422	$39.44	$39.45	$39.40
Purchase #4	$224.99	11.530%	$250.9313	$250.93	$250.95	$250.90
Purchase #5	$74.59	5.215%	$78.4799	$78.48	$78.50	$78.50
Purchase #6	$91.77	8.803%	$99.8485	$99.85	$99.85	$99.80
Purchase #7	$118.64	13.690%	$134.8818	$134.88	$134.90	$134.90
7 purchase totals =	$879.41		$959.3729	$959.37	$959.45	$959.20