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	$18.64	13.555%	$21.1667	$21.17	$21.15	$21.20
Purchase #2	$52.96	12.124%	$59.3809	$59.38	$59.40	$59.40
Purchase #3	$98.71	5.787%	$104.4223	$104.42	$104.40	$104.40
Purchase #4	$91.38	4.385%	$95.387	$95.39	$95.40	$95.40
Purchase #5	$83.54	3.766%	$86.6861	$86.69	$86.70	$86.70
Purchase #6	$131.93	5.366%	$139.0094	$139.01	$139.00	$139.00
Purchase #7	$86.94	13.586%	$98.7517	$98.75	$98.75	$98.80
7 purchase totals =	$564.10		$604.8041	$604.81	$604.80	$604.90