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	$115.80	10.166%	$127.5722	$127.57	$127.55	$127.60
Purchase #2	$71.62	3.497%	$74.1246	$74.12	$74.10	$74.10
Purchase #3	$140.72	8.239%	$152.3139	$152.31	$152.30	$152.30
Purchase #4	$142.66	12.664%	$160.7265	$160.73	$160.75	$160.70
Purchase #5	$19.74	4.156%	$20.5604	$20.56	$20.55	$20.60
Purchase #6	$166.95	5.301%	$175.8	$175.80	$175.80	$175.80
Purchase #7	$40.84	7.269%	$43.8087	$43.81	$43.80	$43.80
7 purchase totals =	$698.33		$754.9063	$754.90	$754.85	$754.90