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	$25.31	7.377%	$27.1771	$27.18	$27.20	$27.20
Purchase #2	$87.65	13.522%	$99.502	$99.50	$99.50	$99.50
Purchase #3	$188.55	9.693%	$206.8262	$206.83	$206.85	$206.80
Purchase #4	$105.69	13.442%	$119.8968	$119.90	$119.90	$119.90
Purchase #5	$164.56	6.742%	$175.6546	$175.65	$175.65	$175.70
Purchase #6	$146.29	4.314%	$152.601	$152.60	$152.60	$152.60
Purchase #7	$65.89	9.852%	$72.3815	$72.38	$72.40	$72.40
7 purchase totals =	$783.94		$854.0392	$854.04	$854.10	$854.10