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	$237.46	7.294%	$254.7803	$254.78	$254.80	$254.80
Purchase #2	$29.77	13.587%	$33.8148	$33.81	$33.80	$33.80
Purchase #3	$146.57	12.748%	$165.2547	$165.25	$165.25	$165.30
Purchase #4	$120.94	5.451%	$127.5324	$127.53	$127.55	$127.50
Purchase #5	$72.84	12.524%	$81.9625	$81.96	$81.95	$82.00
Purchase #6	$178.73	6.635%	$190.5887	$190.59	$190.60	$190.60
Purchase #7	$33.41	9.861%	$36.7046	$36.70	$36.70	$36.70
7 purchase totals =	$819.72		$890.6380	$890.62	$890.65	$890.70