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	$148.27	13.612%	$168.4525	$168.45	$168.45	$168.50
Purchase #2	$180.60	10.213%	$199.0447	$199.04	$199.05	$199.00
Purchase #3	$49.50	9.348%	$54.1273	$54.13	$54.15	$54.10
Purchase #4	$146.90	5.592%	$155.1146	$155.11	$155.10	$155.10
Purchase #5	$166.42	6.658%	$177.5002	$177.50	$177.50	$177.50
Purchase #6	$32.68	12.665%	$36.8189	$36.82	$36.80	$36.80
Purchase #7	$84.43	5.809%	$89.3345	$89.33	$89.35	$89.30
7 purchase totals =	$808.80		$880.3927	$880.38	$880.40	$880.30