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	$209.96	10.104%	$231.1744	$231.17	$231.15	$231.20
Purchase #2	$38.58	3.812%	$40.0507	$40.05	$40.05	$40.10
Purchase #3	$87.91	13.628%	$99.8904	$99.89	$99.90	$99.90
Purchase #4	$71.77	5.293%	$75.5688	$75.57	$75.55	$75.60
Purchase #5	$100.49	7.857%	$108.3855	$108.39	$108.40	$108.40
Purchase #6	$66.62	4.146%	$69.3821	$69.38	$69.40	$69.40
Purchase #7	$64.71	11.346%	$72.052	$72.05	$72.05	$72.10
7 purchase totals =	$640.04		$696.5039	$696.50	$696.50	$696.70