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	$90.31	9.262%	$98.6745	$98.67	$98.65	$98.70
Purchase #2	$109.50	4.719%	$114.6673	$114.67	$114.65	$114.70
Purchase #3	$133.44	5.270%	$140.4723	$140.47	$140.45	$140.50
Purchase #4	$19.97	11.368%	$22.2402	$22.24	$22.25	$22.20
Purchase #5	$72.89	13.311%	$82.5924	$82.59	$82.60	$82.60
Purchase #6	$169.96	12.360%	$190.9671	$190.97	$190.95	$191.00
Purchase #7	$177.66	9.465%	$194.4755	$194.48	$194.50	$194.50
7 purchase totals =	$773.73		$844.0893	$844.09	$844.05	$844.20