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	$130.46	11.510%	$145.4759	$145.48	$145.50	$145.50
Purchase #2	$45.60	4.420%	$47.6155	$47.62	$47.60	$47.60
Purchase #3	$143.87	11.654%	$160.6366	$160.64	$160.65	$160.60
Purchase #4	$86.26	11.473%	$96.1566	$96.16	$96.15	$96.20
Purchase #5	$186.39	12.119%	$208.9786	$208.98	$209.00	$209.00
Purchase #6	$47.42	4.613%	$49.6075	$49.61	$49.60	$49.60
Purchase #7	$173.94	13.227%	$196.947	$196.95	$196.95	$196.90
7 purchase totals =	$813.94		$905.4177	$905.44	$905.45	$905.40