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	$34.45	12.504%	$38.7576	$38.76	$38.75	$38.80
Purchase #2	$144.79	5.387%	$152.5898	$152.59	$152.60	$152.60
Purchase #3	$76.48	12.866%	$86.3199	$86.32	$86.30	$86.30
Purchase #4	$64.72	4.692%	$67.7567	$67.76	$67.75	$67.80
Purchase #5	$116.34	9.304%	$127.1643	$127.16	$127.15	$127.20
Purchase #6	$185.31	9.227%	$202.4086	$202.41	$202.40	$202.40
Purchase #7	$186.41	3.750%	$193.4004	$193.40	$193.40	$193.40
7 purchase totals =	$808.50		$868.3973	$868.40	$868.35	$868.50