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	$100.55	4.868%	$105.4448	$105.44	$105.45	$105.40
Purchase #2	$41.41	8.573%	$44.9601	$44.96	$44.95	$45.00
Purchase #3	$213.92	11.453%	$238.4203	$238.42	$238.40	$238.40
Purchase #4	$99.38	5.290%	$104.6372	$104.64	$104.65	$104.60
Purchase #5	$70.62	11.803%	$78.9553	$78.96	$78.95	$79.00
Purchase #6	$82.85	11.208%	$92.1358	$92.14	$92.15	$92.10
Purchase #7	$187.45	4.346%	$195.5966	$195.60	$195.60	$195.60
7 purchase totals =	$796.18		$860.1501	$860.16	$860.15	$860.10