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	$25.90	13.770%	$29.4664	$29.47	$29.45	$29.50
Purchase #2	$202.72	9.663%	$222.3088	$222.31	$222.30	$222.30
Purchase #3	$174.27	10.641%	$192.8141	$192.81	$192.80	$192.80
Purchase #4	$47.42	7.689%	$51.0661	$51.07	$51.05	$51.10
Purchase #5	$129.40	3.802%	$134.3198	$134.32	$134.30	$134.30
Purchase #6	$137.27	6.854%	$146.6785	$146.68	$146.70	$146.70
Purchase #7	$87.42	13.820%	$99.5014	$99.50	$99.50	$99.50
7 purchase totals =	$804.40		$876.1551	$876.16	$876.10	$876.20