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	$6.98	12.179%	$7.8301	$7.83	$7.85	$7.80
Purchase #2	$105.33	6.189%	$111.8489	$111.85	$111.85	$111.80
Purchase #3	$61.74	13.419%	$70.0249	$70.02	$70.00	$70.00
Purchase #4	$55.86	7.278%	$59.9255	$59.93	$59.95	$59.90
Purchase #5	$37.28	7.335%	$40.0145	$40.01	$40.00	$40.00
Purchase #6	$182.25	3.857%	$189.2794	$189.28	$189.30	$189.30
Purchase #7	$55.98	10.298%	$61.7448	$61.74	$61.75	$61.70
7 purchase totals =	$505.42		$540.6681	$540.66	$540.70	$540.50