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	$37.48	7.490%	$40.2873	$40.29	$40.30	$40.30
Purchase #2	$50.64	5.663%	$53.5077	$53.51	$53.50	$53.50
Purchase #3	$204.94	10.465%	$226.387	$226.39	$226.40	$226.40
Purchase #4	$167.31	4.693%	$175.1619	$175.16	$175.15	$175.20
Purchase #5	$125.82	12.600%	$141.6733	$141.67	$141.65	$141.70
Purchase #6	$167.77	8.239%	$181.5926	$181.59	$181.60	$181.60
Purchase #7	$35.95	7.242%	$38.5535	$38.55	$38.55	$38.60
7 purchase totals =	$789.91		$857.1633	$857.16	$857.15	$857.30