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	$34.50	12.798%	$38.9153	$38.92	$38.90	$38.90
Purchase #2	$225.48	7.288%	$241.913	$241.91	$241.90	$241.90
Purchase #3	$191.38	11.239%	$212.8892	$212.89	$212.90	$212.90
Purchase #4	$33.39	4.242%	$34.8064	$34.81	$34.80	$34.80
Purchase #5	$139.76	5.269%	$147.124	$147.12	$147.10	$147.10
Purchase #6	$144.33	5.430%	$152.1671	$152.17	$152.15	$152.20
Purchase #7	$151.45	10.419%	$167.2296	$167.23	$167.25	$167.20
7 purchase totals =	$920.29		$995.0446	$995.05	$995.00	$995.00