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	$92.62	13.567%	$105.1858	$105.19	$105.20	$105.20
Purchase #2	$18.74	11.327%	$20.8627	$20.86	$20.85	$20.90
Purchase #3	$162.73	3.345%	$168.1733	$168.17	$168.15	$168.20
Purchase #4	$231.33	4.633%	$242.0475	$242.05	$242.05	$242.00
Purchase #5	$136.45	3.750%	$141.5669	$141.57	$141.55	$141.60
Purchase #6	$19.96	12.527%	$22.4604	$22.46	$22.45	$22.50
Purchase #7	$218.40	9.390%	$238.9078	$238.91	$238.90	$238.90
7 purchase totals =	$880.23		$939.2044	$939.21	$939.15	$939.30