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	$94.59	5.284%	$99.5881	$99.59	$99.60	$99.60
Purchase #2	$182.45	12.630%	$205.4934	$205.49	$205.50	$205.50
Purchase #3	$57.55	13.517%	$65.329	$65.33	$65.35	$65.30
Purchase #4	$31.91	5.858%	$33.7793	$33.78	$33.80	$33.80
Purchase #5	$109.73	4.445%	$114.6075	$114.61	$114.60	$114.60
Purchase #6	$120.68	13.553%	$137.0358	$137.04	$137.05	$137.00
Purchase #7	$166.72	7.619%	$179.4224	$179.42	$179.40	$179.40
7 purchase totals =	$763.63		$835.2555	$835.26	$835.30	$835.20