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	$82.42	9.489%	$90.2408	$90.24	$90.25	$90.20
Purchase #2	$111.61	4.276%	$116.3824	$116.38	$116.40	$116.40
Purchase #3	$201.87	8.127%	$218.276	$218.28	$218.30	$218.30
Purchase #4	$224.34	6.343%	$238.5699	$238.57	$238.55	$238.60
Purchase #5	$170.42	11.715%	$190.3847	$190.38	$190.40	$190.40
Purchase #6	$20.57	8.526%	$22.3238	$22.32	$22.30	$22.30
Purchase #7	$102.81	7.366%	$110.383	$110.38	$110.40	$110.40
7 purchase totals =	$914.04		$986.5606	$986.55	$986.60	$986.60