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	$109.57	13.109%	$123.9335	$123.93	$123.95	$123.90
Purchase #2	$148.40	12.843%	$167.459	$167.46	$167.45	$167.50
Purchase #3	$123.92	12.379%	$139.2601	$139.26	$139.25	$139.30
Purchase #4	$214.89	9.566%	$235.4464	$235.45	$235.45	$235.40
Purchase #5	$170.92	9.178%	$186.607	$186.61	$186.60	$186.60
Purchase #6	$140.87	8.501%	$152.8454	$152.85	$152.85	$152.80
Purchase #7	$233.55	3.117%	$240.8298	$240.83	$240.85	$240.80
7 purchase totals =	$1,142.12		$1,246.3812	$1,246.39	$1,246.40	$1,246.30