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	$224.77	13.660%	$255.4736	$255.47	$255.45	$255.50
Purchase #2	$37.61	10.577%	$41.588	$41.59	$41.60	$41.60
Purchase #3	$249.88	13.429%	$283.4364	$283.44	$283.45	$283.40
Purchase #4	$65.96	5.333%	$69.4776	$69.48	$69.50	$69.50
Purchase #5	$28.46	9.532%	$31.1728	$31.17	$31.15	$31.20
Purchase #6	$90.46	6.831%	$96.6393	$96.64	$96.65	$96.60
Purchase #7	$124.28	13.773%	$141.3971	$141.40	$141.40	$141.40
7 purchase totals =	$821.42		$919.1848	$919.19	$919.20	$919.20