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	$215.69	8.105%	$233.1717	$233.17	$233.15	$233.20
Purchase #2	$117.46	4.828%	$123.131	$123.13	$123.15	$123.10
Purchase #3	$33.61	11.705%	$37.5441	$37.54	$37.55	$37.50
Purchase #4	$135.68	8.579%	$147.32	$147.32	$147.30	$147.30
Purchase #5	$113.47	12.580%	$127.7445	$127.74	$127.75	$127.70
Purchase #6	$120.45	9.470%	$131.8566	$131.86	$131.85	$131.90
Purchase #7	$18.33	12.250%	$20.5754	$20.58	$20.60	$20.60
7 purchase totals =	$754.69		$821.3433	$821.34	$821.35	$821.30