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	$26.48	11.792%	$29.6025	$29.60	$29.60	$29.60
Purchase #2	$31.62	3.470%	$32.7172	$32.72	$32.70	$32.70
Purchase #3	$166.83	3.200%	$172.1686	$172.17	$172.15	$172.20
Purchase #4	$216.76	10.541%	$239.6087	$239.61	$239.60	$239.60
Purchase #5	$183.42	3.868%	$190.5147	$190.51	$190.50	$190.50
Purchase #6	$186.47	4.771%	$195.3665	$195.37	$195.35	$195.40
Purchase #7	$40.91	7.316%	$43.903	$43.90	$43.90	$43.90
7 purchase totals =	$852.49		$903.8812	$903.88	$903.80	$903.90