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	$7.68	12.420%	$8.6339	$8.63	$8.65	$8.60
Purchase #2	$169.42	12.655%	$190.8601	$190.86	$190.85	$190.90
Purchase #3	$33.40	5.248%	$35.1528	$35.15	$35.15	$35.20
Purchase #4	$124.52	12.798%	$140.4561	$140.46	$140.45	$140.50
Purchase #5	$234.38	12.319%	$263.2533	$263.25	$263.25	$263.30
Purchase #6	$42.41	7.434%	$45.5628	$45.56	$45.55	$45.60
Purchase #7	$63.56	5.330%	$66.9477	$66.95	$66.95	$66.90
7 purchase totals =	$675.37		$750.8667	$750.86	$750.85	$751.00