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	$231.37	12.345%	$259.9326	$259.93	$259.95	$259.90
Purchase #2	$159.43	5.368%	$167.9882	$167.99	$168.00	$168.00
Purchase #3	$237.60	7.124%	$254.5266	$254.53	$254.55	$254.50
Purchase #4	$188.69	13.249%	$213.6895	$213.69	$213.70	$213.70
Purchase #5	$203.50	9.112%	$222.0429	$222.04	$222.05	$222.00
Purchase #6	$216.83	11.499%	$241.7633	$241.76	$241.75	$241.80
Purchase #7	$177.89	10.514%	$196.5934	$196.59	$196.60	$196.60
7 purchase totals =	$1,415.31		$1,556.5365	$1,556.53	$1,556.60	$1,556.50