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	$76.69	7.676%	$82.5767	$82.58	$82.60	$82.60
Purchase #2	$206.78	7.510%	$222.3092	$222.31	$222.30	$222.30
Purchase #3	$52.27	13.818%	$59.4927	$59.49	$59.50	$59.50
Purchase #4	$45.79	12.242%	$51.3956	$51.40	$51.40	$51.40
Purchase #5	$214.54	10.541%	$237.1547	$237.15	$237.15	$237.20
Purchase #6	$13.61	11.390%	$15.1602	$15.16	$15.15	$15.20
Purchase #7	$117.62	4.401%	$122.7965	$122.80	$122.80	$122.80
7 purchase totals =	$727.30		$790.8856	$790.89	$790.90	$791.00