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	$51.86	6.145%	$55.0468	$55.05	$55.05	$55.00
Purchase #2	$190.42	4.221%	$198.4576	$198.46	$198.45	$198.50
Purchase #3	$40.33	7.382%	$43.3072	$43.31	$43.30	$43.30
Purchase #4	$198.93	6.333%	$211.5282	$211.53	$211.55	$211.50
Purchase #5	$69.50	9.785%	$76.3006	$76.30	$76.30	$76.30
Purchase #6	$146.27	12.166%	$164.0652	$164.07	$164.05	$164.10
Purchase #7	$46.83	11.143%	$52.0483	$52.05	$52.05	$52.00
7 purchase totals =	$744.14		$800.7539	$800.77	$800.75	$800.70