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	$73.84	10.209%	$81.3783	$81.38	$81.40	$81.40
Purchase #2	$53.42	10.475%	$59.0157	$59.02	$59.00	$59.00
Purchase #3	$221.44	12.419%	$248.9406	$248.94	$248.95	$248.90
Purchase #4	$246.36	3.707%	$255.4926	$255.49	$255.50	$255.50
Purchase #5	$137.74	7.639%	$148.262	$148.26	$148.25	$148.30
Purchase #6	$70.52	11.731%	$78.7927	$78.79	$78.80	$78.80
Purchase #7	$124.92	10.338%	$137.8342	$137.83	$137.85	$137.80
7 purchase totals =	$928.24		$1,009.7161	$1,009.71	$1,009.75	$1,009.70