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	$104.25	13.107%	$117.914	$117.91	$117.90	$117.90
Purchase #2	$223.67	4.839%	$234.4934	$234.49	$234.50	$234.50
Purchase #3	$36.73	9.512%	$40.2238	$40.22	$40.20	$40.20
Purchase #4	$98.59	6.106%	$104.6099	$104.61	$104.60	$104.60
Purchase #5	$177.62	12.490%	$199.8047	$199.80	$199.80	$199.80
Purchase #6	$222.85	7.167%	$238.8217	$238.82	$238.80	$238.80
Purchase #7	$147.92	5.486%	$156.0349	$156.03	$156.05	$156.00
7 purchase totals =	$1,011.63		$1,091.9024	$1,091.88	$1,091.85	$1,091.80