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	$18.30	11.282%	$20.3646	$20.36	$20.35	$20.40
Purchase #2	$76.77	7.355%	$82.4164	$82.42	$82.40	$82.40
Purchase #3	$92.48	10.385%	$102.084	$102.08	$102.10	$102.10
Purchase #4	$204.85	4.859%	$214.8037	$214.80	$214.80	$214.80
Purchase #5	$38.86	12.631%	$43.7684	$43.77	$43.75	$43.80
Purchase #6	$173.88	4.263%	$181.2925	$181.29	$181.30	$181.30
Purchase #7	$42.62	7.274%	$45.7202	$45.72	$45.70	$45.70
7 purchase totals =	$647.76		$690.4498	$690.44	$690.40	$690.50