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	$65.83	12.310%	$73.9337	$73.93	$73.95	$73.90
Purchase #2	$16.35	12.364%	$18.3715	$18.37	$18.35	$18.40
Purchase #3	$192.96	9.598%	$211.4803	$211.48	$211.50	$211.50
Purchase #4	$74.75	9.810%	$82.083	$82.08	$82.10	$82.10
Purchase #5	$116.42	13.500%	$132.1367	$132.14	$132.15	$132.10
Purchase #6	$212.88	8.238%	$230.4171	$230.42	$230.40	$230.40
Purchase #7	$47.87	11.687%	$53.4646	$53.46	$53.45	$53.50
7 purchase totals =	$727.06		$801.8869	$801.88	$801.90	$801.90