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	$132.55	7.807%	$142.8982	$142.90	$142.90	$142.90
Purchase #2	$40.33	13.792%	$45.8923	$45.89	$45.90	$45.90
Purchase #3	$49.28	13.363%	$55.8653	$55.87	$55.85	$55.90
Purchase #4	$51.67	9.471%	$56.5637	$56.56	$56.55	$56.60
Purchase #5	$173.95	7.692%	$187.3302	$187.33	$187.35	$187.30
Purchase #6	$60.74	12.769%	$68.4959	$68.50	$68.50	$68.50
Purchase #7	$248.95	12.765%	$280.7285	$280.73	$280.75	$280.70
7 purchase totals =	$757.47		$837.7741	$837.78	$837.80	$837.80