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	$35.40	6.749%	$37.7891	$37.79	$37.80	$37.80
Purchase #2	$214.59	6.443%	$228.416	$228.42	$228.40	$228.40
Purchase #3	$34.29	3.142%	$35.3674	$35.37	$35.35	$35.40
Purchase #4	$29.54	7.739%	$31.8261	$31.83	$31.85	$31.80
Purchase #5	$51.95	3.257%	$53.642	$53.64	$53.65	$53.60
Purchase #6	$54.82	4.770%	$57.4349	$57.43	$57.45	$57.40
Purchase #7	$231.25	13.257%	$261.9068	$261.91	$261.90	$261.90
7 purchase totals =	$651.84		$706.3823	$706.39	$706.40	$706.30