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	$36.93	10.546%	$40.8246	$40.82	$40.80	$40.80
Purchase #2	$244.66	5.667%	$258.5249	$258.52	$258.50	$258.50
Purchase #3	$222.94	5.558%	$235.331	$235.33	$235.35	$235.30
Purchase #4	$181.66	4.405%	$189.6621	$189.66	$189.65	$189.70
Purchase #5	$145.28	7.816%	$156.6351	$156.64	$156.65	$156.60
Purchase #6	$188.57	10.654%	$208.6602	$208.66	$208.65	$208.70
Purchase #7	$63.49	4.265%	$66.1978	$66.20	$66.20	$66.20
7 purchase totals =	$1,083.53		$1,155.8357	$1,155.83	$1,155.80	$1,155.80