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	$52.74	13.404%	$59.8093	$59.81	$59.80	$59.80
Purchase #2	$117.92	3.864%	$122.4764	$122.48	$122.50	$122.50
Purchase #3	$79.52	5.531%	$83.9183	$83.92	$83.90	$83.90
Purchase #4	$100.57	3.564%	$104.1543	$104.15	$104.15	$104.20
Purchase #5	$174.85	5.744%	$184.8934	$184.89	$184.90	$184.90
Purchase #6	$155.61	9.303%	$170.0864	$170.09	$170.10	$170.10
Purchase #7	$100.83	10.780%	$111.6995	$111.70	$111.70	$111.70
7 purchase totals =	$782.04		$837.0376	$837.04	$837.05	$837.10