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	$59.35	13.642%	$67.4465	$67.45	$67.45	$67.40
Purchase #2	$154.32	6.487%	$164.3307	$164.33	$164.35	$164.30
Purchase #3	$82.30	9.865%	$90.4189	$90.42	$90.40	$90.40
Purchase #4	$44.51	4.706%	$46.6046	$46.60	$46.60	$46.60
Purchase #5	$10.28	3.211%	$10.6101	$10.61	$10.60	$10.60
Purchase #6	$173.82	8.651%	$188.8572	$188.86	$188.85	$188.90
Purchase #7	$44.48	11.515%	$49.6019	$49.60	$49.60	$49.60
7 purchase totals =	$569.06		$617.8699	$617.87	$617.85	$617.80