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	$103.70	4.275%	$108.1332	$108.13	$108.15	$108.10
Purchase #2	$37.33	3.530%	$38.6477	$38.65	$38.65	$38.60
Purchase #3	$125.38	7.622%	$134.9365	$134.94	$134.95	$134.90
Purchase #4	$7.70	3.434%	$7.9644	$7.96	$7.95	$8.00
Purchase #5	$85.40	4.735%	$89.4437	$89.44	$89.45	$89.40
Purchase #6	$94.46	7.210%	$101.2706	$101.27	$101.25	$101.30
Purchase #7	$91.65	3.212%	$94.5938	$94.59	$94.60	$94.60
7 purchase totals =	$545.62		$574.9899	$574.98	$575.00	$574.90