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	$24.85	11.527%	$27.7145	$27.71	$27.70	$27.70
Purchase #2	$157.42	4.422%	$164.3811	$164.38	$164.40	$164.40
Purchase #3	$134.51	3.790%	$139.6079	$139.61	$139.60	$139.60
Purchase #4	$130.53	4.382%	$136.2498	$136.25	$136.25	$136.20
Purchase #5	$220.71	6.247%	$234.4978	$234.50	$234.50	$234.50
Purchase #6	$99.30	5.430%	$104.692	$104.69	$104.70	$104.70
Purchase #7	$30.98	4.133%	$32.2604	$32.26	$32.25	$32.30
7 purchase totals =	$798.30		$839.4035	$839.40	$839.40	$839.40