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	$98.39	11.589%	$109.7924	$109.79	$109.80	$109.80
Purchase #2	$32.27	6.131%	$34.2485	$34.25	$34.25	$34.20
Purchase #3	$138.67	5.682%	$146.5492	$146.55	$146.55	$146.50
Purchase #4	$179.44	11.787%	$200.5906	$200.59	$200.60	$200.60
Purchase #5	$132.57	5.579%	$139.9661	$139.97	$139.95	$140.00
Purchase #6	$14.89	5.525%	$15.7127	$15.71	$15.70	$15.70
Purchase #7	$106.57	12.643%	$120.0436	$120.04	$120.05	$120.00
7 purchase totals =	$702.80		$766.9031	$766.90	$766.90	$766.80