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	$29.80	10.353%	$32.8852	$32.89	$32.90	$32.90
Purchase #2	$58.59	13.328%	$66.3989	$66.40	$66.40	$66.40
Purchase #3	$234.27	8.574%	$254.3563	$254.36	$254.35	$254.40
Purchase #4	$237.56	4.219%	$247.5827	$247.58	$247.60	$247.60
Purchase #5	$228.55	7.438%	$245.5495	$245.55	$245.55	$245.50
Purchase #6	$98.27	10.535%	$108.6227	$108.62	$108.60	$108.60
Purchase #7	$236.25	8.297%	$255.8517	$255.85	$255.85	$255.90
7 purchase totals =	$1,123.29		$1,211.2470	$1,211.25	$1,211.25	$1,211.30