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	$90.94	10.430%	$100.425	$100.43	$100.45	$100.40
Purchase #2	$182.77	5.253%	$192.3709	$192.37	$192.35	$192.40
Purchase #3	$100.68	6.508%	$107.2323	$107.23	$107.25	$107.20
Purchase #4	$233.68	4.147%	$243.3707	$243.37	$243.35	$243.40
Purchase #5	$173.31	8.198%	$187.518	$187.52	$187.50	$187.50
Purchase #6	$104.96	8.400%	$113.7766	$113.78	$113.80	$113.80
Purchase #7	$204.54	8.279%	$221.4739	$221.47	$221.45	$221.50
7 purchase totals =	$1,090.88		$1,166.1674	$1,166.17	$1,166.15	$1,166.20