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	$29.59	12.632%	$33.3278	$33.33	$33.35	$33.30
Purchase #2	$217.69	9.510%	$238.3923	$238.39	$238.40	$238.40
Purchase #3	$132.61	7.840%	$143.0066	$143.01	$143.00	$143.00
Purchase #4	$55.27	3.438%	$57.1702	$57.17	$57.15	$57.20
Purchase #5	$235.88	11.825%	$263.7728	$263.77	$263.75	$263.80
Purchase #6	$210.41	10.716%	$232.9575	$232.96	$232.95	$233.00
Purchase #7	$38.88	5.318%	$40.9476	$40.95	$40.95	$40.90
7 purchase totals =	$920.33		$1,009.5748	$1,009.58	$1,009.55	$1,009.60