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	$28.83	3.776%	$29.9186	$29.92	$29.90	$29.90
Purchase #2	$127.87	10.649%	$141.4869	$141.49	$141.50	$141.50
Purchase #3	$135.90	13.753%	$154.5903	$154.59	$154.60	$154.60
Purchase #4	$78.28	6.724%	$83.5435	$83.54	$83.55	$83.50
Purchase #5	$100.97	8.321%	$109.3717	$109.37	$109.35	$109.40
Purchase #6	$125.47	7.515%	$134.8991	$134.90	$134.90	$134.90
Purchase #7	$130.73	12.444%	$146.998	$147.00	$147.00	$147.00
7 purchase totals =	$728.05		$800.8081	$800.81	$800.80	$800.80