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	$18.39	13.151%	$20.8085	$20.81	$20.80	$20.80
Purchase #2	$78.96	9.607%	$86.5457	$86.55	$86.55	$86.50
Purchase #3	$176.77	13.295%	$200.2716	$200.27	$200.25	$200.30
Purchase #4	$139.74	12.273%	$156.8903	$156.89	$156.90	$156.90
Purchase #5	$43.51	11.622%	$48.5667	$48.57	$48.55	$48.60
Purchase #6	$91.85	7.166%	$98.432	$98.43	$98.45	$98.40
Purchase #7	$90.99	12.676%	$102.5239	$102.52	$102.50	$102.50
7 purchase totals =	$640.21		$714.0387	$714.04	$714.00	$714.00