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	$19.43	3.581%	$20.1258	$20.13	$20.15	$20.10
Purchase #2	$132.39	3.333%	$136.8026	$136.80	$136.80	$136.80
Purchase #3	$50.80	8.323%	$55.0281	$55.03	$55.05	$55.00
Purchase #4	$122.60	8.167%	$132.6127	$132.61	$132.60	$132.60
Purchase #5	$241.79	7.777%	$260.594	$260.59	$260.60	$260.60
Purchase #6	$64.34	10.443%	$71.059	$71.06	$71.05	$71.10
Purchase #7	$233.43	13.321%	$264.5252	$264.53	$264.55	$264.50
7 purchase totals =	$864.78		$940.7474	$940.75	$940.80	$940.70