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	$227.51	6.764%	$242.8988	$242.90	$242.90	$242.90
Purchase #2	$30.28	7.667%	$32.6016	$32.60	$32.60	$32.60
Purchase #3	$72.37	13.754%	$82.3238	$82.32	$82.30	$82.30
Purchase #4	$91.41	12.309%	$102.6617	$102.66	$102.65	$102.70
Purchase #5	$102.98	8.641%	$111.8785	$111.88	$111.90	$111.90
Purchase #6	$20.93	12.855%	$23.6206	$23.62	$23.60	$23.60
Purchase #7	$116.83	9.841%	$128.3272	$128.33	$128.35	$128.30
7 purchase totals =	$662.31		$724.3122	$724.31	$724.30	$724.30