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	$49.42	4.167%	$51.4793	$51.48	$51.50	$51.50
Purchase #2	$189.99	13.350%	$215.3537	$215.35	$215.35	$215.40
Purchase #3	$238.25	8.663%	$258.8896	$258.89	$258.90	$258.90
Purchase #4	$84.99	6.312%	$90.3546	$90.35	$90.35	$90.40
Purchase #5	$53.74	10.362%	$59.3085	$59.31	$59.30	$59.30
Purchase #6	$250.80	11.483%	$279.5994	$279.60	$279.60	$279.60
Purchase #7	$183.68	11.834%	$205.4167	$205.42	$205.40	$205.40
7 purchase totals =	$1,050.87		$1,160.4018	$1,160.40	$1,160.40	$1,160.50