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	$137.32	8.226%	$148.6159	$148.62	$148.60	$148.60
Purchase #2	$126.92	7.184%	$136.0379	$136.04	$136.05	$136.00
Purchase #3	$202.85	12.106%	$227.407	$227.41	$227.40	$227.40
Purchase #4	$174.57	9.459%	$191.0826	$191.08	$191.10	$191.10
Purchase #5	$238.25	13.648%	$270.7664	$270.77	$270.75	$270.80
Purchase #6	$167.89	11.657%	$187.4609	$187.46	$187.45	$187.50
Purchase #7	$66.37	9.355%	$72.5789	$72.58	$72.60	$72.60
7 purchase totals =	$1,114.17		$1,233.9496	$1,233.96	$1,233.95	$1,234.00