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	$75.61	3.194%	$78.025	$78.03	$78.05	$78.00
Purchase #2	$92.45	13.823%	$105.2294	$105.23	$105.25	$105.20
Purchase #3	$178.42	5.314%	$187.9012	$187.90	$187.90	$187.90
Purchase #4	$83.58	3.369%	$86.3958	$86.40	$86.40	$86.40
Purchase #5	$213.86	6.405%	$227.5577	$227.56	$227.55	$227.60
Purchase #6	$211.73	7.553%	$227.722	$227.72	$227.70	$227.70
Purchase #7	$133.93	9.187%	$146.2341	$146.23	$146.25	$146.20
7 purchase totals =	$989.58		$1,059.0652	$1,059.07	$1,059.10	$1,059.00