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	$92.27	7.417%	$99.1137	$99.11	$99.10	$99.10
Purchase #2	$63.81	13.223%	$72.2476	$72.25	$72.25	$72.20
Purchase #3	$105.50	11.808%	$117.9574	$117.96	$117.95	$118.00
Purchase #4	$55.42	11.140%	$61.5938	$61.59	$61.60	$61.60
Purchase #5	$121.98	4.832%	$127.8741	$127.87	$127.85	$127.90
Purchase #6	$220.37	13.182%	$249.4192	$249.42	$249.40	$249.40
Purchase #7	$162.46	7.725%	$175.01	$175.01	$175.00	$175.00
7 purchase totals =	$821.81		$903.2158	$903.21	$903.15	$903.20