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	$101.73	6.631%	$108.4757	$108.48	$108.50	$108.50
Purchase #2	$71.51	6.775%	$76.3548	$76.35	$76.35	$76.40
Purchase #3	$218.79	5.132%	$230.0183	$230.02	$230.00	$230.00
Purchase #4	$105.38	11.873%	$117.8918	$117.89	$117.90	$117.90
Purchase #5	$223.39	3.434%	$231.0612	$231.06	$231.05	$231.10
Purchase #6	$239.42	6.641%	$255.3199	$255.32	$255.30	$255.30
Purchase #7	$78.93	13.361%	$89.4758	$89.48	$89.50	$89.50
7 purchase totals =	$1,039.15		$1,108.5975	$1,108.60	$1,108.60	$1,108.70