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	$84.27	6.367%	$89.6355	$89.64	$89.65	$89.60
Purchase #2	$56.86	8.207%	$61.5265	$61.53	$61.55	$61.50
Purchase #3	$60.25	11.469%	$67.1601	$67.16	$67.15	$67.20
Purchase #4	$153.58	10.387%	$169.5324	$169.53	$169.55	$169.50
Purchase #5	$152.49	10.458%	$168.4374	$168.44	$168.45	$168.40
Purchase #6	$11.39	11.576%	$12.7085	$12.71	$12.70	$12.70
Purchase #7	$128.99	10.152%	$142.0851	$142.09	$142.10	$142.10
7 purchase totals =	$647.83		$711.0855	$711.10	$711.15	$711.00