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	$134.89	4.558%	$141.0383	$141.04	$141.05	$141.00
Purchase #2	$53.55	7.398%	$57.5116	$57.51	$57.50	$57.50
Purchase #3	$97.91	8.788%	$106.5143	$106.51	$106.50	$106.50
Purchase #4	$170.53	5.305%	$179.5766	$179.58	$179.60	$179.60
Purchase #5	$117.93	12.522%	$132.6972	$132.70	$132.70	$132.70
Purchase #6	$97.72	12.160%	$109.6028	$109.60	$109.60	$109.60
Purchase #7	$148.27	9.712%	$162.67	$162.67	$162.65	$162.70
7 purchase totals =	$820.80		$889.6108	$889.61	$889.60	$889.60