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	$124.94	5.134%	$131.3544	$131.35	$131.35	$131.40
Purchase #2	$127.72	11.393%	$142.2711	$142.27	$142.25	$142.30
Purchase #3	$80.92	11.777%	$90.4499	$90.45	$90.45	$90.40
Purchase #4	$240.97	8.663%	$261.8452	$261.85	$261.85	$261.80
Purchase #5	$35.33	9.360%	$38.6369	$38.64	$38.65	$38.60
Purchase #6	$153.75	12.261%	$172.6013	$172.60	$172.60	$172.60
Purchase #7	$40.71	6.382%	$43.3081	$43.31	$43.30	$43.30
7 purchase totals =	$804.34		$880.4669	$880.47	$880.45	$880.40