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	$90.58	10.569%	$100.1534	$100.15	$100.15	$100.20
Purchase #2	$204.41	13.386%	$231.7723	$231.77	$231.75	$231.80
Purchase #3	$88.73	10.629%	$98.1611	$98.16	$98.15	$98.20
Purchase #4	$199.66	12.585%	$224.7872	$224.79	$224.80	$224.80
Purchase #5	$231.27	3.483%	$239.3251	$239.33	$239.35	$239.30
Purchase #6	$80.57	5.855%	$85.2874	$85.29	$85.30	$85.30
Purchase #7	$100.36	4.788%	$105.1652	$105.17	$105.15	$105.20
7 purchase totals =	$995.58		$1,084.6517	$1,084.66	$1,084.65	$1,084.80