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	$154.77	10.808%	$171.4975	$171.50	$171.50	$171.50
Purchase #2	$84.35	7.805%	$90.9335	$90.93	$90.95	$90.90
Purchase #3	$71.38	6.269%	$75.8548	$75.85	$75.85	$75.90
Purchase #4	$177.57	12.222%	$199.2726	$199.27	$199.25	$199.30
Purchase #5	$110.48	6.800%	$117.9926	$117.99	$118.00	$118.00
Purchase #6	$84.37	6.867%	$90.1637	$90.16	$90.15	$90.20
Purchase #7	$102.98	13.433%	$116.8133	$116.81	$116.80	$116.80
7 purchase totals =	$785.90		$862.5280	$862.51	$862.50	$862.60