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	$234.89	9.632%	$257.5146	$257.51	$257.50	$257.50
Purchase #2	$117.91	11.509%	$131.4803	$131.48	$131.50	$131.50
Purchase #3	$53.43	10.469%	$59.0236	$59.02	$59.00	$59.00
Purchase #4	$109.95	12.801%	$124.0247	$124.02	$124.00	$124.00
Purchase #5	$120.99	6.149%	$128.4297	$128.43	$128.45	$128.40
Purchase #6	$159.55	11.716%	$178.2429	$178.24	$178.25	$178.20
Purchase #7	$55.49	6.817%	$59.2728	$59.27	$59.25	$59.30
7 purchase totals =	$852.21		$937.9886	$937.97	$937.95	$937.90