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	$21.84	12.171%	$24.4981	$24.50	$24.50	$24.50
Purchase #2	$189.59	9.344%	$207.3053	$207.31	$207.30	$207.30
Purchase #3	$60.25	12.631%	$67.8602	$67.86	$67.85	$67.90
Purchase #4	$95.47	3.349%	$98.6673	$98.67	$98.65	$98.70
Purchase #5	$104.25	7.413%	$111.9781	$111.98	$112.00	$112.00
Purchase #6	$152.56	3.576%	$158.0155	$158.02	$158.00	$158.00
Purchase #7	$89.79	5.203%	$94.4618	$94.46	$94.45	$94.50
7 purchase totals =	$713.75		$762.7863	$762.80	$762.75	$762.90