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	$79.61	13.495%	$90.3534	$90.35	$90.35	$90.40
Purchase #2	$88.54	12.807%	$99.8793	$99.88	$99.90	$99.90
Purchase #3	$228.48	10.627%	$252.7606	$252.76	$252.75	$252.80
Purchase #4	$42.27	6.308%	$44.9364	$44.94	$44.95	$44.90
Purchase #5	$194.63	3.583%	$201.6036	$201.60	$201.60	$201.60
Purchase #6	$160.32	10.762%	$177.5736	$177.57	$177.55	$177.60
Purchase #7	$216.48	7.857%	$233.4888	$233.49	$233.50	$233.50
7 purchase totals =	$1,010.33		$1,100.5957	$1,100.59	$1,100.60	$1,100.70