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	$21.81	3.550%	$22.5843	$22.58	$22.60	$22.60
Purchase #2	$144.73	5.393%	$152.5353	$152.54	$152.55	$152.50
Purchase #3	$157.99	10.119%	$173.977	$173.98	$174.00	$174.00
Purchase #4	$89.33	8.606%	$97.0177	$97.02	$97.00	$97.00
Purchase #5	$59.56	9.328%	$65.1158	$65.12	$65.10	$65.10
Purchase #6	$179.90	9.275%	$196.5857	$196.59	$196.60	$196.60
Purchase #7	$233.56	7.756%	$251.6749	$251.67	$251.65	$251.70
7 purchase totals =	$886.88		$959.4907	$959.50	$959.50	$959.50