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	$6.83	6.663%	$7.2851	$7.29	$7.30	$7.30
Purchase #2	$132.46	5.646%	$139.9387	$139.94	$139.95	$139.90
Purchase #3	$174.55	9.353%	$190.8757	$190.88	$190.90	$190.90
Purchase #4	$44.50	6.296%	$47.3017	$47.30	$47.30	$47.30
Purchase #5	$55.98	10.595%	$61.9111	$61.91	$61.90	$61.90
Purchase #6	$240.47	5.436%	$253.5419	$253.54	$253.55	$253.50
Purchase #7	$86.81	11.827%	$97.077	$97.08	$97.10	$97.10
7 purchase totals =	$741.60		$797.9312	$797.94	$798.00	$797.90