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	$100.61	11.541%	$112.2214	$112.22	$112.20	$112.20
Purchase #2	$216.33	3.464%	$223.8237	$223.82	$223.80	$223.80
Purchase #3	$45.93	6.440%	$48.8879	$48.89	$48.90	$48.90
Purchase #4	$158.48	11.516%	$176.7306	$176.73	$176.75	$176.70
Purchase #5	$58.58	9.861%	$64.3566	$64.36	$64.35	$64.40
Purchase #6	$102.62	5.777%	$108.5484	$108.55	$108.55	$108.50
Purchase #7	$61.38	10.390%	$67.7574	$67.76	$67.75	$67.80
7 purchase totals =	$743.93		$802.3260	$802.33	$802.30	$802.30