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	$17.76	7.816%	$19.1481	$19.15	$19.15	$19.10
Purchase #2	$126.37	12.847%	$142.6048	$142.60	$142.60	$142.60
Purchase #3	$36.71	11.440%	$40.9096	$40.91	$40.90	$40.90
Purchase #4	$154.34	9.242%	$168.6041	$168.60	$168.60	$168.60
Purchase #5	$227.31	4.481%	$237.4958	$237.50	$237.50	$237.50
Purchase #6	$97.37	8.295%	$105.4468	$105.45	$105.45	$105.40
Purchase #7	$108.81	11.395%	$121.2089	$121.21	$121.20	$121.20
7 purchase totals =	$768.67		$835.4181	$835.42	$835.40	$835.30