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	$184.55	10.276%	$203.5144	$203.51	$203.50	$203.50
Purchase #2	$247.42	13.809%	$281.5862	$281.59	$281.60	$281.60
Purchase #3	$13.83	13.119%	$15.6444	$15.64	$15.65	$15.60
Purchase #4	$78.65	13.816%	$89.5163	$89.52	$89.50	$89.50
Purchase #5	$94.36	5.717%	$99.7546	$99.75	$99.75	$99.80
Purchase #6	$16.64	13.861%	$18.9465	$18.95	$18.95	$18.90
Purchase #7	$34.60	6.388%	$36.8102	$36.81	$36.80	$36.80
7 purchase totals =	$670.05		$745.7726	$745.77	$745.75	$745.70