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	$246.33	10.826%	$272.9977	$273.00	$273.00	$273.00
Purchase #2	$105.67	10.449%	$116.7115	$116.71	$116.70	$116.70
Purchase #3	$113.84	12.700%	$128.2977	$128.30	$128.30	$128.30
Purchase #4	$136.65	3.314%	$141.1786	$141.18	$141.20	$141.20
Purchase #5	$123.38	6.674%	$131.6144	$131.61	$131.60	$131.60
Purchase #6	$207.81	3.621%	$215.3348	$215.33	$215.35	$215.30
Purchase #7	$144.44	12.164%	$162.0097	$162.01	$162.00	$162.00
7 purchase totals =	$1,078.12		$1,168.1444	$1,168.14	$1,168.15	$1,168.10