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	$77.60	3.306%	$80.1655	$80.17	$80.15	$80.20
Purchase #2	$13.69	3.707%	$14.1975	$14.20	$14.20	$14.20
Purchase #3	$41.50	9.291%	$45.3558	$45.36	$45.35	$45.40
Purchase #4	$115.82	13.837%	$131.846	$131.85	$131.85	$131.80
Purchase #5	$200.68	6.450%	$213.6239	$213.62	$213.60	$213.60
Purchase #6	$104.96	4.109%	$109.2728	$109.27	$109.25	$109.30
Purchase #7	$42.79	7.381%	$45.9483	$45.95	$45.95	$45.90
7 purchase totals =	$597.04		$640.4098	$640.42	$640.35	$640.40