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	$31.85	11.407%	$35.4831	$35.48	$35.50	$35.50
Purchase #2	$210.33	3.810%	$218.3436	$218.34	$218.35	$218.30
Purchase #3	$214.64	7.383%	$230.4869	$230.49	$230.50	$230.50
Purchase #4	$172.78	4.202%	$180.0402	$180.04	$180.05	$180.00
Purchase #5	$108.58	6.729%	$115.8863	$115.89	$115.90	$115.90
Purchase #6	$234.72	6.727%	$250.5096	$250.51	$250.50	$250.50
Purchase #7	$187.88	6.702%	$200.4717	$200.47	$200.45	$200.50
7 purchase totals =	$1,160.78		$1,231.2214	$1,231.22	$1,231.25	$1,231.20