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	$36.84	8.354%	$39.9176	$39.92	$39.90	$39.90
Purchase #2	$64.99	12.211%	$72.9259	$72.93	$72.95	$72.90
Purchase #3	$249.41	11.119%	$277.1419	$277.14	$277.15	$277.10
Purchase #4	$56.52	4.472%	$59.0476	$59.05	$59.05	$59.00
Purchase #5	$138.90	9.822%	$152.5428	$152.54	$152.55	$152.50
Purchase #6	$168.56	3.276%	$174.082	$174.08	$174.10	$174.10
Purchase #7	$27.32	9.442%	$29.8996	$29.90	$29.90	$29.90
7 purchase totals =	$742.54		$805.5574	$805.56	$805.60	$805.40