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	$70.50	11.752%	$78.7852	$78.79	$78.80	$78.80
Purchase #2	$197.95	13.644%	$224.9583	$224.96	$224.95	$225.00
Purchase #3	$203.98	9.594%	$223.5498	$223.55	$223.55	$223.50
Purchase #4	$151.51	11.277%	$168.5958	$168.60	$168.60	$168.60
Purchase #5	$176.94	4.454%	$184.8209	$184.82	$184.80	$184.80
Purchase #6	$217.76	10.323%	$240.2394	$240.24	$240.25	$240.20
Purchase #7	$208.60	10.174%	$229.823	$229.82	$229.80	$229.80
7 purchase totals =	$1,227.24		$1,350.7724	$1,350.78	$1,350.75	$1,350.70