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	$90.86	11.571%	$101.3734	$101.37	$101.35	$101.40
Purchase #2	$92.78	7.674%	$99.8999	$99.90	$99.90	$99.90
Purchase #3	$153.82	5.375%	$162.0878	$162.09	$162.10	$162.10
Purchase #4	$29.64	12.600%	$33.3746	$33.37	$33.35	$33.40
Purchase #5	$166.51	6.564%	$177.4397	$177.44	$177.45	$177.40
Purchase #6	$55.75	6.765%	$59.5215	$59.52	$59.50	$59.50
Purchase #7	$66.69	13.443%	$75.6551	$75.66	$75.65	$75.70
7 purchase totals =	$656.05		$709.3520	$709.35	$709.30	$709.40