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	$43.45	4.721%	$45.5013	$45.50	$45.50	$45.50
Purchase #2	$84.75	7.843%	$91.3969	$91.40	$91.40	$91.40
Purchase #3	$16.86	8.688%	$18.3248	$18.32	$18.30	$18.30
Purchase #4	$40.29	5.173%	$42.3742	$42.37	$42.35	$42.40
Purchase #5	$48.54	5.265%	$51.0956	$51.10	$51.10	$51.10
Purchase #6	$123.69	12.477%	$139.1228	$139.12	$139.10	$139.10
Purchase #7	$126.83	7.837%	$136.7697	$136.77	$136.75	$136.80
7 purchase totals =	$484.41		$524.5853	$524.58	$524.50	$524.60