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	$99.70	3.230%	$102.9203	$102.92	$102.90	$102.90
Purchase #2	$69.33	13.102%	$78.4136	$78.41	$78.40	$78.40
Purchase #3	$221.69	8.141%	$239.7378	$239.74	$239.75	$239.70
Purchase #4	$90.54	10.206%	$99.7805	$99.78	$99.80	$99.80
Purchase #5	$110.98	6.542%	$118.2403	$118.24	$118.25	$118.20
Purchase #6	$46.78	12.194%	$52.4844	$52.48	$52.50	$52.50
Purchase #7	$87.88	6.510%	$93.601	$93.60	$93.60	$93.60
7 purchase totals =	$726.90		$785.1779	$785.17	$785.20	$785.10