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	$239.95	13.765%	$272.9791	$272.98	$273.00	$273.00
Purchase #2	$76.25	8.195%	$82.4987	$82.50	$82.50	$82.50
Purchase #3	$33.98	10.745%	$37.6312	$37.63	$37.65	$37.60
Purchase #4	$48.75	5.850%	$51.6019	$51.60	$51.60	$51.60
Purchase #5	$119.96	8.769%	$130.4793	$130.48	$130.50	$130.50
Purchase #6	$202.86	13.188%	$229.6132	$229.61	$229.60	$229.60
Purchase #7	$67.96	4.461%	$70.9917	$70.99	$71.00	$71.00
7 purchase totals =	$789.71		$875.7951	$875.79	$875.85	$875.80