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	$47.31	11.766%	$52.8765	$52.88	$52.90	$52.90
Purchase #2	$128.81	4.336%	$134.3952	$134.40	$134.40	$134.40
Purchase #3	$197.55	12.537%	$222.3168	$222.32	$222.30	$222.30
Purchase #4	$31.86	8.139%	$34.4531	$34.45	$34.45	$34.50
Purchase #5	$148.85	6.609%	$158.6875	$158.69	$158.70	$158.70
Purchase #6	$39.30	5.330%	$41.3947	$41.39	$41.40	$41.40
Purchase #7	$139.75	13.809%	$159.0481	$159.05	$159.05	$159.00
7 purchase totals =	$733.43		$803.1719	$803.18	$803.20	$803.20