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	$36.68	4.472%	$38.3203	$38.32	$38.30	$38.30
Purchase #2	$74.31	5.252%	$78.2128	$78.21	$78.20	$78.20
Purchase #3	$210.43	12.670%	$237.0915	$237.09	$237.10	$237.10
Purchase #4	$195.96	13.569%	$222.5498	$222.55	$222.55	$222.50
Purchase #5	$16.94	11.328%	$18.859	$18.86	$18.85	$18.90
Purchase #6	$165.79	7.454%	$178.148	$178.15	$178.15	$178.10
Purchase #7	$66.78	8.638%	$72.5485	$72.55	$72.55	$72.50
7 purchase totals =	$766.89		$845.7299	$845.73	$845.70	$845.60