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	$178.43	12.110%	$200.0379	$200.04	$200.05	$200.00
Purchase #2	$44.74	8.300%	$48.4534	$48.45	$48.45	$48.50
Purchase #3	$42.51	9.523%	$46.5582	$46.56	$46.55	$46.60
Purchase #4	$198.92	9.320%	$217.4593	$217.46	$217.45	$217.50
Purchase #5	$157.40	5.162%	$165.525	$165.53	$165.55	$165.50
Purchase #6	$59.72	7.449%	$64.1685	$64.17	$64.15	$64.20
Purchase #7	$26.95	8.690%	$29.292	$29.29	$29.30	$29.30
7 purchase totals =	$708.67		$771.4943	$771.50	$771.50	$771.60