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	$31.89	7.127%	$34.1628	$34.16	$34.15	$34.20
Purchase #2	$72.46	8.825%	$78.8546	$78.85	$78.85	$78.90
Purchase #3	$95.87	13.639%	$108.9457	$108.95	$108.95	$108.90
Purchase #4	$115.55	10.570%	$127.7636	$127.76	$127.75	$127.80
Purchase #5	$11.70	13.805%	$13.3152	$13.32	$13.30	$13.30
Purchase #6	$50.46	6.140%	$53.5582	$53.56	$53.55	$53.60
Purchase #7	$101.31	8.628%	$110.051	$110.05	$110.05	$110.10
7 purchase totals =	$479.24		$526.6511	$526.65	$526.60	$526.80