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	$33.60	8.789%	$36.5531	$36.55	$36.55	$36.60
Purchase #2	$53.82	3.159%	$55.5202	$55.52	$55.50	$55.50
Purchase #3	$227.89	13.847%	$259.4459	$259.45	$259.45	$259.40
Purchase #4	$40.73	4.205%	$42.4427	$42.44	$42.45	$42.40
Purchase #5	$250.36	12.157%	$280.7963	$280.80	$280.80	$280.80
Purchase #6	$65.99	5.463%	$69.595	$69.60	$69.60	$69.60
Purchase #7	$158.50	7.424%	$170.267	$170.27	$170.25	$170.30
7 purchase totals =	$830.89		$914.6202	$914.63	$914.60	$914.60