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	$144.63	12.343%	$162.4817	$162.48	$162.50	$162.50
Purchase #2	$127.69	10.768%	$141.4397	$141.44	$141.45	$141.40
Purchase #3	$223.89	13.521%	$254.1622	$254.16	$254.15	$254.20
Purchase #4	$38.63	12.467%	$43.446	$43.45	$43.45	$43.40
Purchase #5	$151.97	11.444%	$169.3614	$169.36	$169.35	$169.40
Purchase #6	$58.75	12.461%	$66.0708	$66.07	$66.05	$66.10
Purchase #7	$87.73	3.582%	$90.8725	$90.87	$90.85	$90.90
7 purchase totals =	$833.29		$927.8343	$927.83	$927.80	$927.90