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	$240.29	13.205%	$272.0203	$272.02	$272.00	$272.00
Purchase #2	$120.45	10.217%	$132.7564	$132.76	$132.75	$132.80
Purchase #3	$227.81	12.111%	$255.4001	$255.40	$255.40	$255.40
Purchase #4	$81.76	9.564%	$89.5795	$89.58	$89.60	$89.60
Purchase #5	$99.57	12.668%	$112.1835	$112.18	$112.20	$112.20
Purchase #6	$170.40	5.635%	$180.002	$180.00	$180.00	$180.00
Purchase #7	$186.45	7.585%	$200.5922	$200.59	$200.60	$200.60
7 purchase totals =	$1,126.73		$1,242.5340	$1,242.53	$1,242.55	$1,242.60