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	$147.93	8.607%	$160.6623	$160.66	$160.65	$160.70
Purchase #2	$167.89	13.648%	$190.8036	$190.80	$190.80	$190.80
Purchase #3	$127.30	11.459%	$141.8873	$141.89	$141.90	$141.90
Purchase #4	$90.40	9.327%	$98.8316	$98.83	$98.85	$98.80
Purchase #5	$37.50	3.832%	$38.937	$38.94	$38.95	$38.90
Purchase #6	$144.42	4.535%	$150.9694	$150.97	$150.95	$151.00
Purchase #7	$51.77	10.497%	$57.2043	$57.20	$57.20	$57.20
7 purchase totals =	$767.21		$839.2955	$839.29	$839.30	$839.30