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	$98.43	8.217%	$106.518	$106.52	$106.50	$106.50
Purchase #2	$78.63	13.279%	$89.0713	$89.07	$89.05	$89.10
Purchase #3	$35.48	11.627%	$39.6053	$39.61	$39.60	$39.60
Purchase #4	$83.78	7.523%	$90.0828	$90.08	$90.10	$90.10
Purchase #5	$102.77	9.676%	$112.714	$112.71	$112.70	$112.70
Purchase #6	$211.92	12.840%	$239.1305	$239.13	$239.15	$239.10
Purchase #7	$116.73	11.515%	$130.1715	$130.17	$130.15	$130.20
7 purchase totals =	$727.74		$807.2934	$807.29	$807.25	$807.30