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	$117.80	5.622%	$124.4227	$124.42	$124.40	$124.40
Purchase #2	$88.74	12.711%	$100.0197	$100.02	$100.00	$100.00
Purchase #3	$119.26	10.300%	$131.5438	$131.54	$131.55	$131.50
Purchase #4	$171.98	10.874%	$190.6811	$190.68	$190.70	$190.70
Purchase #5	$69.73	5.125%	$73.3037	$73.30	$73.30	$73.30
Purchase #6	$154.93	9.119%	$169.0581	$169.06	$169.05	$169.10
Purchase #7	$236.50	7.857%	$255.0818	$255.08	$255.10	$255.10
7 purchase totals =	$958.94		$1,044.1109	$1,044.10	$1,044.10	$1,044.10