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	$250.34	12.361%	$281.2845	$281.28	$281.30	$281.30
Purchase #2	$129.33	10.272%	$142.6148	$142.61	$142.60	$142.60
Purchase #3	$14.71	13.238%	$16.6573	$16.66	$16.65	$16.70
Purchase #4	$82.55	9.530%	$90.417	$90.42	$90.40	$90.40
Purchase #5	$168.79	7.153%	$180.8635	$180.86	$180.85	$180.90
Purchase #6	$199.78	12.193%	$224.1392	$224.14	$224.15	$224.10
Purchase #7	$73.45	13.421%	$83.3077	$83.31	$83.30	$83.30
7 purchase totals =	$918.95		$1,019.2840	$1,019.28	$1,019.25	$1,019.30