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	$71.81	9.414%	$78.5702	$78.57	$78.55	$78.60
Purchase #2	$35.95	5.763%	$38.0218	$38.02	$38.00	$38.00
Purchase #3	$77.35	6.769%	$82.5858	$82.59	$82.60	$82.60
Purchase #4	$85.44	8.693%	$92.8673	$92.87	$92.85	$92.90
Purchase #5	$72.65	10.564%	$80.3247	$80.32	$80.30	$80.30
Purchase #6	$14.80	12.295%	$16.6197	$16.62	$16.60	$16.60
Purchase #7	$217.55	6.446%	$231.5733	$231.57	$231.55	$231.60
7 purchase totals =	$575.55		$620.5628	$620.56	$620.45	$620.60