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	$11.85	12.423%	$13.3221	$13.32	$13.30	$13.30
Purchase #2	$69.48	4.535%	$72.6309	$72.63	$72.65	$72.60
Purchase #3	$128.45	6.294%	$136.5346	$136.53	$136.55	$136.50
Purchase #4	$168.47	6.857%	$180.022	$180.02	$180.00	$180.00
Purchase #5	$123.68	3.548%	$128.0682	$128.07	$128.05	$128.10
Purchase #6	$136.84	3.146%	$141.145	$141.15	$141.15	$141.10
Purchase #7	$79.91	12.355%	$89.7829	$89.78	$89.80	$89.80
7 purchase totals =	$718.68		$761.5057	$761.50	$761.50	$761.40