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	$50.74	12.491%	$57.0779	$57.08	$57.10	$57.10
Purchase #2	$55.55	9.280%	$60.705	$60.71	$60.70	$60.70
Purchase #3	$135.96	4.176%	$141.6377	$141.64	$141.65	$141.60
Purchase #4	$90.43	6.781%	$96.5621	$96.56	$96.55	$96.60
Purchase #5	$49.75	3.628%	$51.5549	$51.55	$51.55	$51.60
Purchase #6	$100.56	8.475%	$109.0825	$109.08	$109.10	$109.10
Purchase #7	$38.56	4.402%	$40.2574	$40.26	$40.25	$40.30
7 purchase totals =	$521.55		$556.8775	$556.88	$556.90	$557.00