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	$155.56	10.604%	$172.0556	$172.06	$172.05	$172.10
Purchase #2	$217.35	11.433%	$242.1996	$242.20	$242.20	$242.20
Purchase #3	$136.25	8.333%	$147.6037	$147.60	$147.60	$147.60
Purchase #4	$96.51	7.620%	$103.8641	$103.86	$103.85	$103.90
Purchase #5	$66.63	7.467%	$71.6053	$71.61	$71.60	$71.60
Purchase #6	$198.43	11.373%	$220.9974	$221.00	$221.00	$221.00
Purchase #7	$19.96	9.102%	$21.7768	$21.78	$21.80	$21.80
7 purchase totals =	$890.69		$980.1025	$980.11	$980.10	$980.20