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	$213.28	11.488%	$237.7816	$237.78	$237.80	$237.80
Purchase #2	$86.54	8.594%	$93.9772	$93.98	$94.00	$94.00
Purchase #3	$83.91	6.531%	$89.3902	$89.39	$89.40	$89.40
Purchase #4	$99.85	4.548%	$104.3912	$104.39	$104.40	$104.40
Purchase #5	$172.65	7.213%	$185.1032	$185.10	$185.10	$185.10
Purchase #6	$69.33	12.550%	$78.0309	$78.03	$78.05	$78.00
Purchase #7	$17.34	8.444%	$18.8042	$18.80	$18.80	$18.80
7 purchase totals =	$742.90		$807.4785	$807.47	$807.55	$807.50