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	$159.82	5.142%	$168.0379	$168.04	$168.05	$168.00
Purchase #2	$206.84	12.171%	$232.0145	$232.01	$232.00	$232.00
Purchase #3	$67.59	7.256%	$72.4943	$72.49	$72.50	$72.50
Purchase #4	$240.42	12.229%	$269.821	$269.82	$269.80	$269.80
Purchase #5	$46.59	4.350%	$48.6167	$48.62	$48.60	$48.60
Purchase #6	$234.53	3.253%	$242.1593	$242.16	$242.15	$242.20
Purchase #7	$223.86	10.291%	$246.8974	$246.90	$246.90	$246.90
7 purchase totals =	$1,179.65		$1,280.0411	$1,280.04	$1,280.00	$1,280.00