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	$177.90	6.227%	$188.9778	$188.98	$189.00	$189.00
Purchase #2	$150.32	5.300%	$158.287	$158.29	$158.30	$158.30
Purchase #3	$87.59	12.508%	$98.5458	$98.55	$98.55	$98.50
Purchase #4	$10.98	12.291%	$12.3296	$12.33	$12.35	$12.30
Purchase #5	$221.31	3.287%	$228.5845	$228.58	$228.60	$228.60
Purchase #6	$62.83	10.223%	$69.2531	$69.25	$69.25	$69.30
Purchase #7	$141.72	7.420%	$152.2356	$152.24	$152.25	$152.20
7 purchase totals =	$852.65		$908.2134	$908.22	$908.30	$908.20