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	$76.71	10.299%	$84.6104	$84.61	$84.60	$84.60
Purchase #2	$102.52	8.383%	$111.1143	$111.11	$111.10	$111.10
Purchase #3	$119.52	3.617%	$123.843	$123.84	$123.85	$123.80
Purchase #4	$22.25	9.618%	$24.39	$24.39	$24.40	$24.40
Purchase #5	$171.70	6.336%	$182.5789	$182.58	$182.60	$182.60
Purchase #6	$51.73	6.107%	$54.8892	$54.89	$54.90	$54.90
Purchase #7	$57.63	13.796%	$65.5806	$65.58	$65.60	$65.60
7 purchase totals =	$602.06		$647.0064	$647.00	$647.05	$647.00