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	$27.39	6.765%	$29.2429	$29.24	$29.25	$29.20
Purchase #2	$104.78	13.282%	$118.6969	$118.70	$118.70	$118.70
Purchase #3	$51.58	11.538%	$57.5313	$57.53	$57.55	$57.50
Purchase #4	$18.70	12.332%	$21.0061	$21.01	$21.00	$21.00
Purchase #5	$168.95	3.836%	$175.4309	$175.43	$175.45	$175.40
Purchase #6	$59.33	4.315%	$61.8901	$61.89	$61.90	$61.90
Purchase #7	$104.31	12.727%	$117.5855	$117.59	$117.60	$117.60
7 purchase totals =	$535.04		$581.3837	$581.39	$581.45	$581.30