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	$137.90	4.300%	$143.8297	$143.83	$143.85	$143.80
Purchase #2	$173.61	3.597%	$179.8548	$179.85	$179.85	$179.90
Purchase #3	$207.68	5.440%	$218.9778	$218.98	$219.00	$219.00
Purchase #4	$40.84	10.537%	$45.1433	$45.14	$45.15	$45.10
Purchase #5	$5.82	4.311%	$6.0709	$6.07	$6.05	$6.10
Purchase #6	$140.45	13.862%	$159.9192	$159.92	$159.90	$159.90
Purchase #7	$120.48	6.518%	$128.3329	$128.33	$128.35	$128.30
7 purchase totals =	$826.78		$882.1286	$882.12	$882.15	$882.10