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	$249.76	6.320%	$265.5448	$265.54	$265.55	$265.50
Purchase #2	$99.88	13.805%	$113.6684	$113.67	$113.65	$113.70
Purchase #3	$67.62	6.732%	$72.1722	$72.17	$72.15	$72.20
Purchase #4	$137.54	7.631%	$148.0357	$148.04	$148.05	$148.00
Purchase #5	$147.33	5.686%	$155.7072	$155.71	$155.70	$155.70
Purchase #6	$212.36	10.446%	$234.5431	$234.54	$234.55	$234.50
Purchase #7	$82.52	4.413%	$86.1616	$86.16	$86.15	$86.20
7 purchase totals =	$997.01		$1,075.8330	$1,075.83	$1,075.80	$1,075.80