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	$106.89	4.214%	$111.3943	$111.39	$111.40	$111.40
Purchase #2	$14.78	7.388%	$15.8719	$15.87	$15.85	$15.90
Purchase #3	$28.56	12.127%	$32.0235	$32.02	$32.00	$32.00
Purchase #4	$210.77	5.108%	$221.5361	$221.54	$221.55	$221.50
Purchase #5	$246.60	8.143%	$266.6806	$266.68	$266.70	$266.70
Purchase #6	$104.63	7.380%	$112.3517	$112.35	$112.35	$112.40
Purchase #7	$126.86	10.408%	$140.0636	$140.06	$140.05	$140.10
7 purchase totals =	$839.09		$899.9217	$899.91	$899.90	$900.00