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	$39.53	8.734%	$42.9826	$42.98	$43.00	$43.00
Purchase #2	$174.86	8.698%	$190.0693	$190.07	$190.05	$190.10
Purchase #3	$39.50	10.446%	$43.6262	$43.63	$43.65	$43.60
Purchase #4	$209.64	13.752%	$238.4697	$238.47	$238.45	$238.50
Purchase #5	$97.89	8.616%	$106.3242	$106.32	$106.30	$106.30
Purchase #6	$181.61	7.246%	$194.7695	$194.77	$194.75	$194.80
Purchase #7	$31.87	3.711%	$33.0527	$33.05	$33.05	$33.10
7 purchase totals =	$774.90		$849.2942	$849.29	$849.25	$849.40