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	$87.98	4.795%	$92.1986	$92.20	$92.20	$92.20
Purchase #2	$100.80	12.153%	$113.0502	$113.05	$113.05	$113.10
Purchase #3	$45.47	4.501%	$47.5166	$47.52	$47.50	$47.50
Purchase #4	$243.78	12.615%	$274.5328	$274.53	$274.55	$274.50
Purchase #5	$145.52	13.652%	$165.3864	$165.39	$165.40	$165.40
Purchase #6	$27.32	8.638%	$29.6799	$29.68	$29.70	$29.70
Purchase #7	$39.67	7.107%	$42.4893	$42.49	$42.50	$42.50
7 purchase totals =	$690.54		$764.8538	$764.86	$764.90	$764.90