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	$38.57	6.144%	$40.9397	$40.94	$40.95	$40.90
Purchase #2	$187.66	9.754%	$205.9644	$205.96	$205.95	$206.00
Purchase #3	$95.51	4.269%	$99.5873	$99.59	$99.60	$99.60
Purchase #4	$104.46	11.836%	$116.8239	$116.82	$116.80	$116.80
Purchase #5	$11.89	12.637%	$13.3925	$13.39	$13.40	$13.40
Purchase #6	$150.28	7.839%	$162.0604	$162.06	$162.05	$162.10
Purchase #7	$206.38	6.537%	$219.8711	$219.87	$219.85	$219.90
7 purchase totals =	$794.75		$858.6393	$858.63	$858.60	$858.70