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	$17.61	7.190%	$18.8762	$18.88	$18.90	$18.90
Purchase #2	$30.45	4.397%	$31.7889	$31.79	$31.80	$31.80
Purchase #3	$163.61	13.650%	$185.9428	$185.94	$185.95	$185.90
Purchase #4	$123.82	6.432%	$131.7841	$131.78	$131.80	$131.80
Purchase #5	$250.93	6.462%	$267.1451	$267.15	$267.15	$267.10
Purchase #6	$240.25	6.175%	$255.0854	$255.09	$255.10	$255.10
Purchase #7	$8.70	6.213%	$9.2405	$9.24	$9.25	$9.20
7 purchase totals =	$835.37		$899.8630	$899.87	$899.95	$899.80