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	$24.81	10.384%	$27.3863	$27.39	$27.40	$27.40
Purchase #2	$88.33	9.429%	$96.6586	$96.66	$96.65	$96.70
Purchase #3	$137.63	7.311%	$147.6921	$147.69	$147.70	$147.70
Purchase #4	$154.53	7.751%	$166.5076	$166.51	$166.50	$166.50
Purchase #5	$105.91	6.229%	$112.5071	$112.51	$112.50	$112.50
Purchase #6	$245.93	4.163%	$256.1681	$256.17	$256.15	$256.20
Purchase #7	$69.73	12.228%	$78.2566	$78.26	$78.25	$78.30
7 purchase totals =	$826.87		$885.1764	$885.19	$885.15	$885.30