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	$34.75	8.169%	$37.5887	$37.59	$37.60	$37.60
Purchase #2	$91.79	7.172%	$98.3732	$98.37	$98.35	$98.40
Purchase #3	$30.39	9.228%	$33.1944	$33.19	$33.20	$33.20
Purchase #4	$54.48	9.123%	$59.4502	$59.45	$59.45	$59.50
Purchase #5	$68.90	13.330%	$78.0844	$78.08	$78.10	$78.10
Purchase #6	$223.77	9.285%	$244.547	$244.55	$244.55	$244.50
Purchase #7	$242.25	12.443%	$272.3932	$272.39	$272.40	$272.40
7 purchase totals =	$746.33		$823.6311	$823.62	$823.65	$823.70