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	$85.28	4.643%	$89.2396	$89.24	$89.25	$89.20
Purchase #2	$132.86	13.691%	$151.0499	$151.05	$151.05	$151.00
Purchase #3	$233.77	13.225%	$264.6861	$264.69	$264.70	$264.70
Purchase #4	$139.76	6.428%	$148.7438	$148.74	$148.75	$148.70
Purchase #5	$228.71	8.278%	$247.6426	$247.64	$247.65	$247.60
Purchase #6	$141.83	4.226%	$147.8237	$147.82	$147.80	$147.80
Purchase #7	$38.44	5.692%	$40.628	$40.63	$40.65	$40.60
7 purchase totals =	$1,000.65		$1,089.8137	$1,089.81	$1,089.85	$1,089.60