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	$94.72	5.305%	$99.7449	$99.74	$99.75	$99.70
Purchase #2	$144.45	9.552%	$158.2479	$158.25	$158.25	$158.20
Purchase #3	$63.90	12.829%	$72.0977	$72.10	$72.10	$72.10
Purchase #4	$46.45	12.594%	$52.2999	$52.30	$52.30	$52.30
Purchase #5	$195.67	10.296%	$215.8162	$215.82	$215.80	$215.80
Purchase #6	$93.74	8.595%	$101.797	$101.80	$101.80	$101.80
Purchase #7	$64.82	12.400%	$72.8577	$72.86	$72.85	$72.90
7 purchase totals =	$703.75		$772.8613	$772.87	$772.85	$772.80