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	$11.53	10.460%	$12.736	$12.74	$12.75	$12.70
Purchase #2	$120.80	9.746%	$132.5732	$132.57	$132.55	$132.60
Purchase #3	$55.25	10.704%	$61.164	$61.16	$61.15	$61.20
Purchase #4	$213.46	12.682%	$240.531	$240.53	$240.55	$240.50
Purchase #5	$82.51	10.307%	$91.0143	$91.01	$91.00	$91.00
Purchase #6	$17.90	4.847%	$18.7676	$18.77	$18.75	$18.80
Purchase #7	$18.41	13.153%	$20.8315	$20.83	$20.85	$20.80
7 purchase totals =	$519.86		$577.6176	$577.61	$577.60	$577.60