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	$137.89	6.268%	$146.5329	$146.53	$146.55	$146.50
Purchase #2	$101.26	12.448%	$113.8648	$113.86	$113.85	$113.90
Purchase #3	$174.70	7.103%	$187.1089	$187.11	$187.10	$187.10
Purchase #4	$54.55	9.371%	$59.6619	$59.66	$59.65	$59.70
Purchase #5	$136.67	3.846%	$141.9263	$141.93	$141.95	$141.90
Purchase #6	$241.56	3.223%	$249.3455	$249.35	$249.35	$249.30
Purchase #7	$101.33	3.639%	$105.0174	$105.02	$105.00	$105.00
7 purchase totals =	$947.96		$1,003.4577	$1,003.46	$1,003.45	$1,003.40