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	$231.85	10.701%	$256.6603	$256.66	$256.65	$256.70
Purchase #2	$12.42	11.127%	$13.802	$13.80	$13.80	$13.80
Purchase #3	$68.58	13.581%	$77.8938	$77.89	$77.90	$77.90
Purchase #4	$183.61	3.329%	$189.7224	$189.72	$189.70	$189.70
Purchase #5	$112.88	6.722%	$120.4678	$120.47	$120.45	$120.50
Purchase #6	$171.76	10.797%	$190.3049	$190.30	$190.30	$190.30
Purchase #7	$115.76	13.584%	$131.4848	$131.48	$131.50	$131.50
7 purchase totals =	$896.86		$980.3360	$980.32	$980.30	$980.40