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	$57.47	3.418%	$59.4343	$59.43	$59.45	$59.40
Purchase #2	$104.65	10.874%	$116.0296	$116.03	$116.05	$116.00
Purchase #3	$82.94	7.788%	$89.3994	$89.40	$89.40	$89.40
Purchase #4	$223.51	10.693%	$247.4099	$247.41	$247.40	$247.40
Purchase #5	$169.60	5.254%	$178.5108	$178.51	$178.50	$178.50
Purchase #6	$90.40	9.126%	$98.6499	$98.65	$98.65	$98.60
Purchase #7	$144.78	9.836%	$159.0206	$159.02	$159.00	$159.00
7 purchase totals =	$873.35		$948.4545	$948.45	$948.45	$948.30