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	$155.46	8.476%	$168.6368	$168.64	$168.65	$168.60
Purchase #2	$137.69	5.592%	$145.3896	$145.39	$145.40	$145.40
Purchase #3	$178.65	12.446%	$200.8848	$200.88	$200.90	$200.90
Purchase #4	$87.67	13.182%	$99.2267	$99.23	$99.25	$99.20
Purchase #5	$26.57	5.230%	$27.9596	$27.96	$27.95	$28.00
Purchase #6	$15.67	8.547%	$17.0093	$17.01	$17.00	$17.00
Purchase #7	$42.68	7.208%	$45.7564	$45.76	$45.75	$45.80
7 purchase totals =	$644.39		$704.8632	$704.87	$704.90	$704.90