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	$53.49	11.659%	$59.7264	$59.73	$59.75	$59.70
Purchase #2	$246.92	12.818%	$278.5702	$278.57	$278.55	$278.60
Purchase #3	$63.68	3.828%	$66.1177	$66.12	$66.10	$66.10
Purchase #4	$67.27	4.527%	$70.3153	$70.32	$70.30	$70.30
Purchase #5	$224.73	13.752%	$255.6349	$255.63	$255.65	$255.60
Purchase #6	$216.97	10.781%	$240.3615	$240.36	$240.35	$240.40
Purchase #7	$7.57	5.332%	$7.9736	$7.97	$7.95	$8.00
7 purchase totals =	$880.63		$978.6996	$978.70	$978.65	$978.70