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	$127.42	3.202%	$131.5	$131.50	$131.50	$131.50
Purchase #2	$178.53	12.504%	$200.8534	$200.85	$200.85	$200.90
Purchase #3	$96.58	4.149%	$100.5871	$100.59	$100.60	$100.60
Purchase #4	$148.28	13.290%	$167.9864	$167.99	$168.00	$168.00
Purchase #5	$173.77	3.250%	$179.4175	$179.42	$179.40	$179.40
Purchase #6	$106.31	4.103%	$110.6719	$110.67	$110.65	$110.70
Purchase #7	$76.76	4.686%	$80.357	$80.36	$80.35	$80.40
7 purchase totals =	$907.65		$971.3733	$971.38	$971.35	$971.50