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	$91.55	12.433%	$102.9324	$102.93	$102.95	$102.90
Purchase #2	$225.81	10.412%	$249.3213	$249.32	$249.30	$249.30
Purchase #3	$54.87	12.132%	$61.5268	$61.53	$61.55	$61.50
Purchase #4	$156.73	8.153%	$169.5082	$169.51	$169.50	$169.50
Purchase #5	$243.62	4.472%	$254.5147	$254.51	$254.50	$254.50
Purchase #6	$122.61	13.726%	$139.4394	$139.44	$139.45	$139.40
Purchase #7	$38.54	7.624%	$41.4783	$41.48	$41.50	$41.50
7 purchase totals =	$933.73		$1,018.7211	$1,018.72	$1,018.75	$1,018.60