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	$208.69	8.728%	$226.9045	$226.90	$226.90	$226.90
Purchase #2	$188.83	13.602%	$214.5147	$214.51	$214.50	$214.50
Purchase #3	$82.32	10.342%	$90.8335	$90.83	$90.85	$90.80
Purchase #4	$145.74	9.743%	$159.9394	$159.94	$159.95	$159.90
Purchase #5	$115.58	6.650%	$123.2661	$123.27	$123.25	$123.30
Purchase #6	$62.53	8.425%	$67.7982	$67.80	$67.80	$67.80
Purchase #7	$41.27	10.606%	$45.6471	$45.65	$45.65	$45.60
7 purchase totals =	$844.96		$928.9035	$928.90	$928.90	$928.80