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	$220.54	8.446%	$239.1668	$239.17	$239.15	$239.20
Purchase #2	$125.36	13.575%	$142.3776	$142.38	$142.40	$142.40
Purchase #3	$132.74	13.206%	$150.2696	$150.27	$150.25	$150.30
Purchase #4	$68.86	5.761%	$72.827	$72.83	$72.85	$72.80
Purchase #5	$79.39	12.546%	$89.3503	$89.35	$89.35	$89.40
Purchase #6	$156.51	3.618%	$162.1725	$162.17	$162.15	$162.20
Purchase #7	$88.50	9.283%	$96.7155	$96.72	$96.70	$96.70
7 purchase totals =	$871.90		$952.8793	$952.89	$952.85	$953.00