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	$131.47	6.289%	$139.7381	$139.74	$139.75	$139.70
Purchase #2	$178.60	11.272%	$198.7318	$198.73	$198.75	$198.70
Purchase #3	$198.78	7.740%	$214.1656	$214.17	$214.15	$214.20
Purchase #4	$134.83	10.546%	$149.0492	$149.05	$149.05	$149.00
Purchase #5	$162.61	3.763%	$168.729	$168.73	$168.75	$168.70
Purchase #6	$56.72	4.569%	$59.3115	$59.31	$59.30	$59.30
Purchase #7	$168.51	11.130%	$187.2652	$187.27	$187.25	$187.30
7 purchase totals =	$1,031.52		$1,116.9904	$1,117.00	$1,117.00	$1,116.90