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	$78.34	6.146%	$83.1548	$83.15	$83.15	$83.20
Purchase #2	$247.72	4.759%	$259.509	$259.51	$259.50	$259.50
Purchase #3	$81.44	4.491%	$85.0975	$85.10	$85.10	$85.10
Purchase #4	$80.28	7.642%	$86.415	$86.42	$86.40	$86.40
Purchase #5	$230.25	4.626%	$240.9014	$240.90	$240.90	$240.90
Purchase #6	$119.25	8.420%	$129.2909	$129.29	$129.30	$129.30
Purchase #7	$241.89	12.591%	$272.3464	$272.35	$272.35	$272.30
7 purchase totals =	$1,079.17		$1,156.7150	$1,156.72	$1,156.70	$1,156.70