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	$18.80	3.667%	$19.4894	$19.49	$19.50	$19.50
Purchase #2	$54.64	8.498%	$59.2833	$59.28	$59.30	$59.30
Purchase #3	$239.36	9.244%	$261.4864	$261.49	$261.50	$261.50
Purchase #4	$204.64	13.264%	$231.7834	$231.78	$231.80	$231.80
Purchase #5	$151.48	3.510%	$156.7969	$156.80	$156.80	$156.80
Purchase #6	$212.82	10.824%	$235.8556	$235.86	$235.85	$235.90
Purchase #7	$108.96	9.723%	$119.5542	$119.55	$119.55	$119.60
7 purchase totals =	$990.70		$1,084.2492	$1,084.25	$1,084.30	$1,084.40