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	$69.31	4.772%	$72.6175	$72.62	$72.60	$72.60
Purchase #2	$79.58	13.439%	$90.2748	$90.27	$90.25	$90.30
Purchase #3	$112.98	3.380%	$116.7987	$116.80	$116.80	$116.80
Purchase #4	$229.41	8.795%	$249.5866	$249.59	$249.60	$249.60
Purchase #5	$249.34	4.654%	$260.9443	$260.94	$260.95	$260.90
Purchase #6	$31.55	6.844%	$33.7093	$33.71	$33.70	$33.70
Purchase #7	$13.41	6.540%	$14.287	$14.29	$14.30	$14.30
7 purchase totals =	$785.58		$838.2182	$838.22	$838.20	$838.20