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	$147.25	12.514%	$165.6769	$165.68	$165.70	$165.70
Purchase #2	$95.67	8.272%	$103.5838	$103.58	$103.60	$103.60
Purchase #3	$112.67	9.316%	$123.1663	$123.17	$123.15	$123.20
Purchase #4	$212.30	13.205%	$240.3342	$240.33	$240.35	$240.30
Purchase #5	$81.81	8.830%	$89.0338	$89.03	$89.05	$89.00
Purchase #6	$197.53	9.466%	$216.2282	$216.23	$216.25	$216.20
Purchase #7	$196.59	9.470%	$215.2071	$215.21	$215.20	$215.20
7 purchase totals =	$1,043.82		$1,153.2303	$1,153.23	$1,153.30	$1,153.20