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	$240.96	12.619%	$271.3667	$271.37	$271.35	$271.40
Purchase #2	$92.78	12.107%	$104.0129	$104.01	$104.00	$104.00
Purchase #3	$158.47	8.289%	$171.6056	$171.61	$171.60	$171.60
Purchase #4	$65.63	9.829%	$72.0808	$72.08	$72.10	$72.10
Purchase #5	$138.73	7.151%	$148.6506	$148.65	$148.65	$148.70
Purchase #6	$123.89	13.832%	$141.0265	$141.03	$141.05	$141.00
Purchase #7	$13.32	4.565%	$13.9281	$13.93	$13.95	$13.90
7 purchase totals =	$833.78		$922.6712	$922.68	$922.70	$922.70