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	$28.92	9.116%	$31.5563	$31.56	$31.55	$31.60
Purchase #2	$76.27	6.710%	$81.3877	$81.39	$81.40	$81.40
Purchase #3	$105.80	6.681%	$112.8685	$112.87	$112.85	$112.90
Purchase #4	$104.79	7.865%	$113.0317	$113.03	$113.05	$113.00
Purchase #5	$143.31	13.669%	$162.899	$162.90	$162.90	$162.90
Purchase #6	$40.39	4.229%	$42.0981	$42.10	$42.10	$42.10
Purchase #7	$20.28	10.428%	$22.3948	$22.39	$22.40	$22.40
7 purchase totals =	$519.76		$566.2361	$566.24	$566.25	$566.30