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	$129.89	5.676%	$137.2626	$137.26	$137.25	$137.30
Purchase #2	$233.97	9.220%	$255.542	$255.54	$255.55	$255.50
Purchase #3	$215.60	3.186%	$222.469	$222.47	$222.45	$222.50
Purchase #4	$104.62	4.420%	$109.2442	$109.24	$109.25	$109.20
Purchase #5	$215.59	10.803%	$238.8802	$238.88	$238.90	$238.90
Purchase #6	$85.41	9.392%	$93.4317	$93.43	$93.45	$93.40
Purchase #7	$164.75	11.109%	$183.0521	$183.05	$183.05	$183.10
7 purchase totals =	$1,149.83		$1,239.8818	$1,239.87	$1,239.90	$1,239.90