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	$247.52	7.800%	$266.8266	$266.83	$266.85	$266.80
Purchase #2	$191.38	12.248%	$214.8202	$214.82	$214.80	$214.80
Purchase #3	$102.38	7.153%	$109.7032	$109.70	$109.70	$109.70
Purchase #4	$196.98	9.409%	$215.5138	$215.51	$215.50	$215.50
Purchase #5	$85.80	4.282%	$89.474	$89.47	$89.45	$89.50
Purchase #6	$18.29	11.107%	$20.3215	$20.32	$20.30	$20.30
Purchase #7	$236.39	12.652%	$266.2981	$266.30	$266.30	$266.30
7 purchase totals =	$1,078.74		$1,182.9574	$1,182.95	$1,182.90	$1,182.90