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	$53.69	10.487%	$59.3205	$59.32	$59.30	$59.30
Purchase #2	$223.39	13.190%	$252.8551	$252.86	$252.85	$252.90
Purchase #3	$123.99	12.343%	$139.2941	$139.29	$139.30	$139.30
Purchase #4	$6.33	13.668%	$7.1952	$7.20	$7.20	$7.20
Purchase #5	$13.50	13.736%	$15.3544	$15.35	$15.35	$15.40
Purchase #6	$123.51	3.535%	$127.8761	$127.88	$127.90	$127.90
Purchase #7	$241.97	3.160%	$249.6163	$249.62	$249.60	$249.60
7 purchase totals =	$786.38		$851.5117	$851.52	$851.50	$851.60