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	$130.31	6.269%	$138.4791	$138.48	$138.50	$138.50
Purchase #2	$110.35	5.655%	$116.5903	$116.59	$116.60	$116.60
Purchase #3	$94.85	11.220%	$105.4922	$105.49	$105.50	$105.50
Purchase #4	$72.59	7.863%	$78.2978	$78.30	$78.30	$78.30
Purchase #5	$206.55	4.747%	$216.3549	$216.35	$216.35	$216.40
Purchase #6	$154.27	6.296%	$163.9828	$163.98	$164.00	$164.00
Purchase #7	$242.39	6.193%	$257.4012	$257.40	$257.40	$257.40
7 purchase totals =	$1,011.31		$1,076.5983	$1,076.59	$1,076.65	$1,076.70