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	$122.96	13.801%	$139.9297	$139.93	$139.95	$139.90
Purchase #2	$53.78	11.766%	$60.1078	$60.11	$60.10	$60.10
Purchase #3	$32.25	3.149%	$33.2656	$33.27	$33.25	$33.30
Purchase #4	$108.26	3.713%	$112.2797	$112.28	$112.30	$112.30
Purchase #5	$227.78	5.811%	$241.0163	$241.02	$241.00	$241.00
Purchase #6	$224.91	7.303%	$241.3352	$241.34	$241.35	$241.30
Purchase #7	$39.98	5.527%	$42.1897	$42.19	$42.20	$42.20
7 purchase totals =	$809.92		$870.1240	$870.14	$870.15	$870.10