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	$227.60	13.414%	$258.1303	$258.13	$258.15	$258.10
Purchase #2	$138.40	7.793%	$149.1855	$149.19	$149.20	$149.20
Purchase #3	$5.91	5.541%	$6.2375	$6.24	$6.25	$6.20
Purchase #4	$168.89	12.771%	$190.4589	$190.46	$190.45	$190.50
Purchase #5	$40.30	6.266%	$42.8252	$42.83	$42.85	$42.80
Purchase #6	$158.88	13.154%	$179.7791	$179.78	$179.80	$179.80
Purchase #7	$19.78	5.628%	$20.8932	$20.89	$20.90	$20.90
7 purchase totals =	$759.76		$847.5097	$847.52	$847.60	$847.50