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	$112.80	9.772%	$123.8228	$123.82	$123.80	$123.80
Purchase #2	$120.55	13.499%	$136.823	$136.82	$136.80	$136.80
Purchase #3	$147.47	7.241%	$158.1483	$158.15	$158.15	$158.10
Purchase #4	$112.47	3.405%	$116.2996	$116.30	$116.30	$116.30
Purchase #5	$13.57	11.498%	$15.1303	$15.13	$15.15	$15.10
Purchase #6	$14.29	7.541%	$15.3676	$15.37	$15.35	$15.40
Purchase #7	$100.72	6.607%	$107.3746	$107.37	$107.35	$107.40
7 purchase totals =	$621.87		$672.9662	$672.96	$672.90	$672.90