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	$18.78	10.621%	$20.7746	$20.77	$20.75	$20.80
Purchase #2	$153.57	9.744%	$168.5339	$168.53	$168.55	$168.50
Purchase #3	$190.28	10.800%	$210.8302	$210.83	$210.85	$210.80
Purchase #4	$147.91	6.244%	$157.1455	$157.15	$157.15	$157.10
Purchase #5	$62.60	4.710%	$65.5485	$65.55	$65.55	$65.50
Purchase #6	$101.46	10.818%	$112.4359	$112.44	$112.45	$112.40
Purchase #7	$48.40	3.460%	$50.0746	$50.07	$50.05	$50.10
7 purchase totals =	$723.00		$785.3432	$785.34	$785.35	$785.20