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	$34.80	7.446%	$37.3912	$37.39	$37.40	$37.40
Purchase #2	$203.80	5.159%	$214.314	$214.31	$214.30	$214.30
Purchase #3	$34.55	5.536%	$36.4627	$36.46	$36.45	$36.50
Purchase #4	$113.73	4.142%	$118.4407	$118.44	$118.45	$118.40
Purchase #5	$70.90	6.426%	$75.456	$75.46	$75.45	$75.50
Purchase #6	$79.55	4.262%	$82.9404	$82.94	$82.95	$82.90
Purchase #7	$78.55	6.644%	$83.7689	$83.77	$83.75	$83.80
7 purchase totals =	$615.88		$648.7739	$648.77	$648.75	$648.80