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	$12.31	7.587%	$13.244	$13.24	$13.25	$13.20
Purchase #2	$177.60	4.623%	$185.8104	$185.81	$185.80	$185.80
Purchase #3	$30.44	12.126%	$34.1312	$34.13	$34.15	$34.10
Purchase #4	$32.82	3.310%	$33.9063	$33.91	$33.90	$33.90
Purchase #5	$21.59	11.593%	$24.0929	$24.09	$24.10	$24.10
Purchase #6	$146.67	7.453%	$157.6013	$157.60	$157.60	$157.60
Purchase #7	$40.87	4.242%	$42.6037	$42.60	$42.60	$42.60
7 purchase totals =	$462.30		$491.3898	$491.38	$491.40	$491.30