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	$49.75	8.864%	$54.1598	$54.16	$54.15	$54.20
Purchase #2	$166.58	3.516%	$172.437	$172.44	$172.45	$172.40
Purchase #3	$130.62	9.151%	$142.573	$142.57	$142.55	$142.60
Purchase #4	$203.78	8.594%	$221.2929	$221.29	$221.30	$221.30
Purchase #5	$20.79	12.392%	$23.3663	$23.37	$23.35	$23.40
Purchase #6	$78.85	8.527%	$85.5735	$85.57	$85.55	$85.60
Purchase #7	$61.74	9.225%	$67.4355	$67.44	$67.45	$67.40
7 purchase totals =	$712.11		$766.8380	$766.84	$766.80	$766.90