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	$28.39	11.223%	$31.5762	$31.58	$31.60	$31.60
Purchase #2	$21.92	7.625%	$23.5914	$23.59	$23.60	$23.60
Purchase #3	$137.46	12.422%	$154.5353	$154.54	$154.55	$154.50
Purchase #4	$210.97	11.196%	$234.5902	$234.59	$234.60	$234.60
Purchase #5	$115.86	9.715%	$127.1158	$127.12	$127.10	$127.10
Purchase #6	$82.98	13.690%	$94.34	$94.34	$94.35	$94.30
Purchase #7	$37.34	8.450%	$40.4952	$40.50	$40.50	$40.50
7 purchase totals =	$634.92		$706.2441	$706.26	$706.30	$706.20