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	$82.67	8.725%	$89.883	$89.88	$89.90	$89.90
Purchase #2	$246.65	12.841%	$278.3223	$278.32	$278.30	$278.30
Purchase #3	$48.31	11.280%	$53.7594	$53.76	$53.75	$53.80
Purchase #4	$94.58	10.431%	$104.4456	$104.45	$104.45	$104.40
Purchase #5	$43.39	3.559%	$44.9343	$44.93	$44.95	$44.90
Purchase #6	$51.70	11.220%	$57.5007	$57.50	$57.50	$57.50
Purchase #7	$232.80	10.380%	$256.9646	$256.96	$256.95	$257.00
7 purchase totals =	$800.10		$885.8099	$885.80	$885.80	$885.80