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	$94.53	6.188%	$100.3795	$100.38	$100.40	$100.40
Purchase #2	$92.78	7.145%	$99.4091	$99.41	$99.40	$99.40
Purchase #3	$198.74	13.483%	$225.5361	$225.54	$225.55	$225.50
Purchase #4	$224.59	11.290%	$249.9462	$249.95	$249.95	$249.90
Purchase #5	$153.62	9.149%	$167.6747	$167.67	$167.65	$167.70
Purchase #6	$97.64	5.609%	$103.1166	$103.12	$103.10	$103.10
Purchase #7	$41.28	13.671%	$46.9234	$46.92	$46.90	$46.90
7 purchase totals =	$903.18		$992.9856	$992.99	$992.95	$992.90