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	$164.43	12.459%	$184.9163	$184.92	$184.90	$184.90
Purchase #2	$40.77	8.369%	$44.182	$44.18	$44.20	$44.20
Purchase #3	$247.29	7.127%	$264.9144	$264.91	$264.90	$264.90
Purchase #4	$19.63	9.686%	$21.5314	$21.53	$21.55	$21.50
Purchase #5	$245.56	3.379%	$253.8575	$253.86	$253.85	$253.90
Purchase #6	$17.33	5.731%	$18.3232	$18.32	$18.30	$18.30
Purchase #7	$166.92	8.783%	$181.5806	$181.58	$181.60	$181.60
7 purchase totals =	$901.93		$969.3054	$969.30	$969.30	$969.30