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	$164.67	8.421%	$178.5369	$178.54	$178.55	$178.50
Purchase #2	$135.58	6.265%	$144.0741	$144.07	$144.05	$144.10
Purchase #3	$210.70	3.825%	$218.7593	$218.76	$218.75	$218.80
Purchase #4	$126.33	13.421%	$143.2847	$143.28	$143.30	$143.30
Purchase #5	$99.35	5.556%	$104.8699	$104.87	$104.85	$104.90
Purchase #6	$56.49	5.138%	$59.3925	$59.39	$59.40	$59.40
Purchase #7	$46.59	8.158%	$50.3908	$50.39	$50.40	$50.40
7 purchase totals =	$839.71		$899.3082	$899.30	$899.30	$899.40