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	$33.91	13.667%	$38.5445	$38.54	$38.55	$38.50
Purchase #2	$92.90	3.373%	$96.0335	$96.03	$96.05	$96.00
Purchase #3	$51.57	9.642%	$56.5424	$56.54	$56.55	$56.50
Purchase #4	$242.68	4.846%	$254.4403	$254.44	$254.45	$254.40
Purchase #5	$35.42	7.815%	$38.1881	$38.19	$38.20	$38.20
Purchase #6	$239.30	13.168%	$270.811	$270.81	$270.80	$270.80
Purchase #7	$47.78	13.640%	$54.2972	$54.30	$54.30	$54.30
7 purchase totals =	$743.56		$808.8570	$808.85	$808.90	$808.70