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	$57.27	4.276%	$59.7189	$59.72	$59.70	$59.70
Purchase #2	$131.35	10.268%	$144.837	$144.84	$144.85	$144.80
Purchase #3	$155.50	5.337%	$163.799	$163.80	$163.80	$163.80
Purchase #4	$52.32	3.209%	$53.9989	$54.00	$54.00	$54.00
Purchase #5	$216.30	3.310%	$223.4595	$223.46	$223.45	$223.50
Purchase #6	$129.50	9.462%	$141.7533	$141.75	$141.75	$141.80
Purchase #7	$170.91	12.497%	$192.2686	$192.27	$192.25	$192.30
7 purchase totals =	$913.15		$979.8352	$979.84	$979.80	$979.90