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	$19.33	4.111%	$20.1247	$20.12	$20.10	$20.10
Purchase #2	$62.45	11.153%	$69.415	$69.42	$69.40	$69.40
Purchase #3	$227.58	12.822%	$256.7603	$256.76	$256.75	$256.80
Purchase #4	$111.85	3.799%	$116.0992	$116.10	$116.10	$116.10
Purchase #5	$164.92	6.271%	$175.2621	$175.26	$175.25	$175.30
Purchase #6	$94.79	9.243%	$103.5514	$103.55	$103.55	$103.60
Purchase #7	$84.83	11.666%	$94.7263	$94.73	$94.75	$94.70
7 purchase totals =	$765.75		$835.9390	$835.94	$835.90	$836.00