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	$236.40	13.699%	$268.7844	$268.78	$268.80	$268.80
Purchase #2	$159.63	8.299%	$172.8777	$172.88	$172.90	$172.90
Purchase #3	$14.77	6.567%	$15.7399	$15.74	$15.75	$15.70
Purchase #4	$228.61	13.223%	$258.8391	$258.84	$258.85	$258.80
Purchase #5	$89.40	6.349%	$95.076	$95.08	$95.10	$95.10
Purchase #6	$208.51	5.631%	$220.2512	$220.25	$220.25	$220.30
Purchase #7	$53.35	12.291%	$59.9072	$59.91	$59.90	$59.90
7 purchase totals =	$990.67		$1,091.4755	$1,091.48	$1,091.55	$1,091.50