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	$36.50	10.819%	$40.4489	$40.45	$40.45	$40.40
Purchase #2	$98.70	9.316%	$107.8949	$107.89	$107.90	$107.90
Purchase #3	$82.81	8.645%	$89.9689	$89.97	$89.95	$90.00
Purchase #4	$126.35	3.347%	$130.5789	$130.58	$130.60	$130.60
Purchase #5	$152.61	6.154%	$162.0016	$162.00	$162.00	$162.00
Purchase #6	$133.38	5.791%	$141.104	$141.10	$141.10	$141.10
Purchase #7	$53.38	3.834%	$55.4266	$55.43	$55.45	$55.40
7 purchase totals =	$683.73		$727.4238	$727.42	$727.45	$727.40