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	$99.86	8.624%	$108.4719	$108.47	$108.45	$108.50
Purchase #2	$139.74	12.291%	$156.9154	$156.92	$156.90	$156.90
Purchase #3	$28.57	10.865%	$31.6741	$31.67	$31.65	$31.70
Purchase #4	$151.98	10.283%	$167.6081	$167.61	$167.60	$167.60
Purchase #5	$40.78	13.539%	$46.3012	$46.30	$46.30	$46.30
Purchase #6	$102.28	4.340%	$106.719	$106.72	$106.70	$106.70
Purchase #7	$51.93	10.851%	$57.5649	$57.56	$57.55	$57.60
7 purchase totals =	$615.14		$675.2546	$675.25	$675.15	$675.30