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	$6.93	13.189%	$7.844	$7.84	$7.85	$7.80
Purchase #2	$79.60	5.415%	$83.9103	$83.91	$83.90	$83.90
Purchase #3	$179.59	5.313%	$189.1316	$189.13	$189.15	$189.10
Purchase #4	$54.72	7.326%	$58.7288	$58.73	$58.75	$58.70
Purchase #5	$223.34	4.473%	$233.33	$233.33	$233.35	$233.30
Purchase #6	$100.96	10.226%	$111.2842	$111.28	$111.30	$111.30
Purchase #7	$97.43	12.677%	$109.7812	$109.78	$109.80	$109.80
7 purchase totals =	$742.57		$794.0101	$794.00	$794.10	$793.90