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	$48.60	6.758%	$51.8844	$51.88	$51.90	$51.90
Purchase #2	$31.99	3.526%	$33.118	$33.12	$33.10	$33.10
Purchase #3	$58.34	11.242%	$64.8986	$64.90	$64.90	$64.90
Purchase #4	$118.70	10.805%	$131.5255	$131.53	$131.55	$131.50
Purchase #5	$91.81	10.164%	$101.1416	$101.14	$101.15	$101.10
Purchase #6	$132.43	4.777%	$138.7562	$138.76	$138.75	$138.80
Purchase #7	$78.28	13.395%	$88.7656	$88.77	$88.75	$88.80
7 purchase totals =	$560.15		$610.0899	$610.10	$610.10	$610.10