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	$210.30	5.630%	$222.1399	$222.14	$222.15	$222.10
Purchase #2	$118.54	11.780%	$132.504	$132.50	$132.50	$132.50
Purchase #3	$92.85	8.639%	$100.8713	$100.87	$100.85	$100.90
Purchase #4	$113.58	6.315%	$120.7526	$120.75	$120.75	$120.80
Purchase #5	$40.32	7.263%	$43.2484	$43.25	$43.25	$43.20
Purchase #6	$153.46	12.314%	$172.3571	$172.36	$172.35	$172.40
Purchase #7	$75.86	11.865%	$84.8608	$84.86	$84.85	$84.90
7 purchase totals =	$804.91		$876.7341	$876.73	$876.70	$876.80