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	$45.39	8.663%	$49.3221	$49.32	$49.30	$49.30
Purchase #2	$53.43	9.615%	$58.5673	$58.57	$58.55	$58.60
Purchase #3	$136.74	6.714%	$145.9207	$145.92	$145.90	$145.90
Purchase #4	$56.55	10.389%	$62.425	$62.43	$62.45	$62.40
Purchase #5	$248.51	12.143%	$278.6866	$278.69	$278.70	$278.70
Purchase #6	$31.38	6.616%	$33.4561	$33.46	$33.45	$33.50
Purchase #7	$199.91	11.359%	$222.6178	$222.62	$222.60	$222.60
7 purchase totals =	$771.91		$850.9956	$851.01	$850.95	$851.00