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	$142.76	9.381%	$156.1523	$156.15	$156.15	$156.20
Purchase #2	$130.93	3.731%	$135.815	$135.82	$135.80	$135.80
Purchase #3	$213.69	4.640%	$223.6052	$223.61	$223.60	$223.60
Purchase #4	$163.29	5.698%	$172.5943	$172.59	$172.60	$172.60
Purchase #5	$167.64	7.782%	$180.6857	$180.69	$180.70	$180.70
Purchase #6	$239.73	8.138%	$259.2392	$259.24	$259.25	$259.20
Purchase #7	$22.78	7.235%	$24.4281	$24.43	$24.45	$24.40
7 purchase totals =	$1,080.82		$1,152.5198	$1,152.53	$1,152.55	$1,152.50