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	$213.71	11.737%	$238.7931	$238.79	$238.80	$238.80
Purchase #2	$37.62	13.496%	$42.6972	$42.70	$42.70	$42.70
Purchase #3	$11.31	8.219%	$12.2396	$12.24	$12.25	$12.20
Purchase #4	$72.50	8.652%	$78.7727	$78.77	$78.75	$78.80
Purchase #5	$60.42	3.258%	$62.3885	$62.39	$62.40	$62.40
Purchase #6	$52.81	4.192%	$55.0238	$55.02	$55.00	$55.00
Purchase #7	$65.81	6.527%	$70.1054	$70.11	$70.10	$70.10
7 purchase totals =	$514.18		$560.0203	$560.02	$560.00	$560.00