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	$122.48	13.706%	$139.2671	$139.27	$139.25	$139.30
Purchase #2	$200.83	11.279%	$223.4816	$223.48	$223.50	$223.50
Purchase #3	$20.52	4.611%	$21.4662	$21.47	$21.45	$21.50
Purchase #4	$102.64	12.138%	$115.0984	$115.10	$115.10	$115.10
Purchase #5	$12.59	11.825%	$14.0788	$14.08	$14.10	$14.10
Purchase #6	$10.90	13.477%	$12.369	$12.37	$12.35	$12.40
Purchase #7	$140.91	4.677%	$147.5004	$147.50	$147.50	$147.50
7 purchase totals =	$610.87		$673.2615	$673.27	$673.25	$673.40