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	$129.56	4.662%	$135.6001	$135.60	$135.60	$135.60
Purchase #2	$154.90	13.769%	$176.2282	$176.23	$176.25	$176.20
Purchase #3	$120.25	9.595%	$131.788	$131.79	$131.80	$131.80
Purchase #4	$85.44	4.636%	$89.401	$89.40	$89.40	$89.40
Purchase #5	$177.96	3.372%	$183.9608	$183.96	$183.95	$184.00
Purchase #6	$86.92	7.470%	$93.4129	$93.41	$93.40	$93.40
Purchase #7	$85.55	5.750%	$90.4691	$90.47	$90.45	$90.50
7 purchase totals =	$840.58		$900.8601	$900.86	$900.85	$900.90