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	$228.52	9.169%	$249.473	$249.47	$249.45	$249.50
Purchase #2	$60.82	4.629%	$63.6354	$63.64	$63.65	$63.60
Purchase #3	$61.66	3.124%	$63.5863	$63.59	$63.60	$63.60
Purchase #4	$226.98	7.290%	$243.5268	$243.53	$243.55	$243.50
Purchase #5	$117.75	11.372%	$131.1405	$131.14	$131.15	$131.10
Purchase #6	$10.32	13.525%	$11.7158	$11.72	$11.70	$11.70
Purchase #7	$63.73	13.432%	$72.2902	$72.29	$72.30	$72.30
7 purchase totals =	$769.78		$835.3680	$835.38	$835.40	$835.30