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	$38.45	4.258%	$40.0872	$40.09	$40.10	$40.10
Purchase #2	$105.75	9.678%	$115.9845	$115.98	$116.00	$116.00
Purchase #3	$158.41	13.140%	$179.2251	$179.23	$179.25	$179.20
Purchase #4	$240.57	7.461%	$258.5189	$258.52	$258.50	$258.50
Purchase #5	$43.62	3.867%	$45.3068	$45.31	$45.30	$45.30
Purchase #6	$242.67	10.759%	$268.7789	$268.78	$268.80	$268.80
Purchase #7	$137.84	10.591%	$152.4386	$152.44	$152.45	$152.40
7 purchase totals =	$967.31		$1,060.3400	$1,060.35	$1,060.40	$1,060.30