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	$80.86	5.187%	$85.0542	$85.05	$85.05	$85.10
Purchase #2	$172.66	4.370%	$180.2052	$180.21	$180.20	$180.20
Purchase #3	$130.69	5.187%	$137.4689	$137.47	$137.45	$137.50
Purchase #4	$140.99	13.233%	$159.6472	$159.65	$159.65	$159.60
Purchase #5	$159.28	13.340%	$180.528	$180.53	$180.55	$180.50
Purchase #6	$98.27	5.679%	$103.8508	$103.85	$103.85	$103.90
Purchase #7	$25.94	10.321%	$28.6173	$28.62	$28.60	$28.60
7 purchase totals =	$808.69		$875.3716	$875.38	$875.35	$875.40