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	$145.77	3.635%	$151.0687	$151.07	$151.05	$151.10
Purchase #2	$116.66	9.549%	$127.7999	$127.80	$127.80	$127.80
Purchase #3	$95.77	4.265%	$99.8546	$99.85	$99.85	$99.90
Purchase #4	$77.72	5.534%	$82.021	$82.02	$82.00	$82.00
Purchase #5	$47.97	10.182%	$52.8543	$52.85	$52.85	$52.90
Purchase #6	$225.38	12.659%	$253.9109	$253.91	$253.90	$253.90
Purchase #7	$127.79	6.609%	$136.2356	$136.24	$136.25	$136.20
7 purchase totals =	$837.06		$903.7450	$903.74	$903.70	$903.80