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	$77.51	7.242%	$83.1233	$83.12	$83.10	$83.10
Purchase #2	$96.99	13.284%	$109.8742	$109.87	$109.85	$109.90
Purchase #3	$129.49	12.299%	$145.416	$145.42	$145.40	$145.40
Purchase #4	$246.50	13.564%	$279.9353	$279.94	$279.95	$279.90
Purchase #5	$212.36	13.870%	$241.8143	$241.81	$241.80	$241.80
Purchase #6	$118.27	10.213%	$130.3489	$130.35	$130.35	$130.30
Purchase #7	$110.73	11.546%	$123.5149	$123.51	$123.50	$123.50
7 purchase totals =	$991.85		$1,114.0269	$1,114.02	$1,113.95	$1,113.90