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	$56.87	4.590%	$59.4803	$59.48	$59.50	$59.50
Purchase #2	$143.44	12.558%	$161.4532	$161.45	$161.45	$161.50
Purchase #3	$96.86	5.596%	$102.2803	$102.28	$102.30	$102.30
Purchase #4	$60.30	4.245%	$62.8597	$62.86	$62.85	$62.90
Purchase #5	$86.88	3.154%	$89.6202	$89.62	$89.60	$89.60
Purchase #6	$191.49	10.274%	$211.1637	$211.16	$211.15	$211.20
Purchase #7	$166.69	6.643%	$177.7632	$177.76	$177.75	$177.80
7 purchase totals =	$802.53		$864.6206	$864.61	$864.60	$864.80