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	$18.71	9.185%	$20.4285	$20.43	$20.45	$20.40
Purchase #2	$142.50	4.201%	$148.4864	$148.49	$148.50	$148.50
Purchase #3	$112.88	9.312%	$123.3914	$123.39	$123.40	$123.40
Purchase #4	$150.30	10.432%	$165.9793	$165.98	$166.00	$166.00
Purchase #5	$169.66	6.689%	$181.0086	$181.01	$181.00	$181.00
Purchase #6	$205.65	11.653%	$229.6144	$229.61	$229.60	$229.60
Purchase #7	$147.71	10.312%	$162.9419	$162.94	$162.95	$162.90
7 purchase totals =	$947.41		$1,031.8505	$1,031.85	$1,031.90	$1,031.80