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	$130.40	3.633%	$135.1374	$135.14	$135.15	$135.10
Purchase #2	$115.96	10.661%	$128.3225	$128.32	$128.30	$128.30
Purchase #3	$171.28	8.219%	$185.3575	$185.36	$185.35	$185.40
Purchase #4	$87.29	12.184%	$97.9254	$97.93	$97.95	$97.90
Purchase #5	$118.38	11.301%	$131.7581	$131.76	$131.75	$131.80
Purchase #6	$113.84	11.670%	$127.1251	$127.13	$127.15	$127.10
Purchase #7	$18.25	9.320%	$19.9509	$19.95	$19.95	$20.00
7 purchase totals =	$755.40		$825.5769	$825.59	$825.60	$825.60