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	$193.37	3.262%	$199.6777	$199.68	$199.70	$199.70
Purchase #2	$86.77	13.594%	$98.5655	$98.57	$98.55	$98.60
Purchase #3	$83.86	9.148%	$91.5315	$91.53	$91.55	$91.50
Purchase #4	$7.94	5.558%	$8.3813	$8.38	$8.40	$8.40
Purchase #5	$150.52	6.783%	$160.7298	$160.73	$160.75	$160.70
Purchase #6	$123.75	3.810%	$128.4649	$128.46	$128.45	$128.50
Purchase #7	$20.75	5.545%	$21.9006	$21.90	$21.90	$21.90
7 purchase totals =	$666.96		$709.2513	$709.25	$709.30	$709.30