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	$38.89	8.315%	$42.1237	$42.12	$42.10	$42.10
Purchase #2	$194.57	12.694%	$219.2687	$219.27	$219.25	$219.30
Purchase #3	$169.92	12.570%	$191.2789	$191.28	$191.30	$191.30
Purchase #4	$29.38	10.160%	$32.365	$32.37	$32.35	$32.40
Purchase #5	$199.49	9.799%	$219.038	$219.04	$219.05	$219.00
Purchase #6	$226.60	4.849%	$237.5878	$237.59	$237.60	$237.60
Purchase #7	$204.90	11.626%	$228.7217	$228.72	$228.70	$228.70
7 purchase totals =	$1,063.75		$1,170.3838	$1,170.39	$1,170.35	$1,170.40