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	$210.44	9.716%	$230.8864	$230.89	$230.90	$230.90
Purchase #2	$34.53	10.855%	$38.2782	$38.28	$38.30	$38.30
Purchase #3	$209.78	10.766%	$232.3649	$232.36	$232.35	$232.40
Purchase #4	$121.82	4.727%	$127.5784	$127.58	$127.60	$127.60
Purchase #5	$98.82	10.801%	$109.4935	$109.49	$109.50	$109.50
Purchase #6	$65.82	10.839%	$72.9542	$72.95	$72.95	$73.00
Purchase #7	$156.60	9.744%	$171.8591	$171.86	$171.85	$171.90
7 purchase totals =	$897.81		$983.4147	$983.41	$983.45	$983.60