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	$35.73	7.618%	$38.4519	$38.45	$38.45	$38.50
Purchase #2	$171.48	12.389%	$192.7247	$192.72	$192.70	$192.70
Purchase #3	$174.37	11.714%	$194.7957	$194.80	$194.80	$194.80
Purchase #4	$9.62	9.193%	$10.5044	$10.50	$10.50	$10.50
Purchase #5	$132.33	13.401%	$150.0635	$150.06	$150.05	$150.10
Purchase #6	$143.44	10.215%	$158.0924	$158.09	$158.10	$158.10
Purchase #7	$152.59	10.196%	$168.1481	$168.15	$168.15	$168.10
7 purchase totals =	$819.56		$912.7807	$912.77	$912.75	$912.80