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	$81.82	4.533%	$85.5289	$85.53	$85.55	$85.50
Purchase #2	$219.78	13.575%	$249.6151	$249.62	$249.60	$249.60
Purchase #3	$231.55	11.238%	$257.5716	$257.57	$257.55	$257.60
Purchase #4	$59.68	5.367%	$62.883	$62.88	$62.90	$62.90
Purchase #5	$186.38	12.382%	$209.4576	$209.46	$209.45	$209.50
Purchase #6	$47.58	9.471%	$52.0863	$52.09	$52.10	$52.10
Purchase #7	$29.38	7.675%	$31.6349	$31.63	$31.65	$31.60
7 purchase totals =	$856.17		$948.7774	$948.78	$948.80	$948.80