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	$127.47	3.407%	$131.8129	$131.81	$131.80	$131.80
Purchase #2	$71.69	6.537%	$76.3764	$76.38	$76.40	$76.40
Purchase #3	$209.93	8.239%	$227.2261	$227.23	$227.25	$227.20
Purchase #4	$170.92	12.793%	$192.7858	$192.79	$192.80	$192.80
Purchase #5	$33.77	10.649%	$37.3662	$37.37	$37.35	$37.40
Purchase #6	$119.72	3.838%	$124.3149	$124.31	$124.30	$124.30
Purchase #7	$106.31	7.174%	$113.9367	$113.94	$113.95	$113.90
7 purchase totals =	$839.81		$903.8190	$903.83	$903.85	$903.80